Package 'MetaboCoreUtils'

Description

addElements Add one chemical formula to another.

Usage

addElements(x, y)

Arguments

Value

character Resulting formula

Author(s)

Michael Witting and Sebastian Gibb

Examples

addElements("C6H12O6", "Na")

addElements("C6H12O6", c("Na", "H2O"))

Description

adductFormula calculates the chemical formulas for the specified adducts of provided chemical formulas.

Usage

adductFormula(formulas, adduct = "[M+H]+", standardize = TRUE)

Arguments

Value

character matrix with formula rows and adducts columns containing all ion formulas. In case an ion can't be generated (eg. [M-NH3+H]+ in a molecule that doesn't have nitrogen), a NA is returned instead.

Author(s)

Roger Gine

See Also

adductNames() for a list of all available predefined adducts and adducts() for the adduct data.frame definition style.

Examples

# Calculate the ion formulas of glucose with adducts [M+H]+, [M+Na]+ and [M+K]+
adductFormula("C6H12O6", c("[M+H]+", "[M+Na]+", "[M+K]+"))

# > "[C6H13O6]+" "[C6H12O6Na]+" "[C6H12O6K]+"

# Use a custom set of adduct definitions (For instance, a iron (Fe2+) adduct)
custom_ads <- data.frame(name = "[M+Fe]2+", mass_multi = 0.5, charge = 2,
                         formula_add = "Fe", formula_sub = "C0",
                         positive = "TRUE")
adductFormula("C6H12O6", custom_ads)

Description

adductNames returns all supported adduct definitions that can be used by mass2mz() and mz2mass().

adducts returns a data.frame with the adduct definitions.

Usage

adductNames(polarity = c("positive", "negative"))

adducts(polarity = c("positive", "negative"))

Arguments

Value

for adductNames: character vector with all valid adduct names for the selected ion mode. For adducts: data.frame with the adduct definitions.

Author(s)

Michael Witting, Johannes Rainer

Examples

## retrieve names of adduct names in positive ion mode
adductNames(polarity = "positive")

## retrieve names of adduct names in negative ion mode
adductNames(polarity = "negative")

Description

Kendrick mass defect analysis is a way to analyze high-resolution MS data in order to identify homologous series. The Kendrick mass (KM) is calculated by choosing a specific molecular fragment (e.g. CH2) and settings its mass to an integer mass. In case of CH2 the mass of 14.01565 would be set to 14.The Kendrick mass defect (KMD) is defined as the difference between the KM and the nominial (integer) KM. All molecules of homologoues series, e.g. only differing in the number of CH2, will have an identical KMD. In an additional step the KMD can be referenced to the mass defect of specific lipid backbone and by this normalize values to the referenced KMD (RKMD). This leads to values of 0 for saturated species or -1, -2, -3, etc for unsaturated species.

Available functoins are:

• calculateKm: calculates the Kendrick mass from an exact mass for a specific molecular fragment, e.g. "CH2".

• calculateKmd: calculates the Kendrick mass defect from an exact mass for a specific molecular fragment, e.g. "CH2".

• calculateRkmd: calculates the referenced Kendrick mass defect from an exact mass for a specific molecular fragment, e.g. "CH2", and a reference KMD.

• isRkmd: Checks if a calculated RKMD falls within a specific error range around an negative integer corresponding the number of double bonds, in case of CH2 as fragment.

Usage

calculateKm(x, fragment = 14/14.01565)

calculateKmd(x, fragment = 14/14.01565)

calculateRkmd(x, fragment = 14/14.01565, rkmd = 0.749206)

isRkmd(x, rkmdTolerance = 0.1)

Arguments

Value

numeric or boolean. All functions, except isRkmd return a numeric with same length as the input corresponding to the KM, KMD or RMKD. isRkmd returns a logical with TRUE or FALSE indicating if the RKMD falls within a specific range around a negative integer corresponding to the number of double bonds.

Author(s)

Michael Witting

Examples

calculateKm(760.5851)

calculateKmd(760.5851)

calculateRkmd(760.5851, rkmd = 0.749206)

isRkmd(calculateRkmd(760.5851, rkmd = 0.749206))

Description

calculateMass calculates the exact mass from a formula. Isotopes are also supported. For isotopes, the isotope type needs to be specified as an element's prefix, e.g. "[13C]" for carbon 13 or "[2H]" for deuterium. A formula with 2 carbon 13 isotopes and 3 carbons would thus contain e.g. "[13C2]C3".

Usage

calculateMass(x)

Arguments

Value

numeric Resulting exact mass.

Author(s)

Michael Witting

Examples

calculateMass("C6H12O6")
calculateMass("NH3")
calculateMass(c("C6H12O6", "NH3"))

## Calculate masses for formulas containing isotope information.
calculateMass(c("C6H12O6", "[13C3]C3H12O6"))

## Calculate mass for a chemical with 5 deuterium.
calculateMass("C11[2H5]H7N2O2")

Description

containsElements checks if one sum formula is contained in another.

Usage

containsElements(x, y)

Arguments

Value

logical TRUE if y is contained in x

Author(s)

Michael Witting and Sebastian Gibb

Examples

containsElements("C6H12O6", "H2O")
containsElements("C6H12O6", "NH3")

Description

convertMtime performs effective mobility scale transformation of CE(-MS) data, which is used to overcome variations of the migration times, caused by differences in the Electroosmotic Flow (EOF) between different runs. In order to monitor the EOF and perform the transformation, neutral or charged EOF markers are spiked into the sample before analysis. The information of the EOF markers (migration time and effective mobility) will be then used to perform the effective mobility transformation of the migration time scale.

Usage

convertMtime(
  x = numeric(),
  rtime = numeric(),
  mobility = numeric(),
  tR = 0,
  U = numeric(),
  L = numeric()
)

Arguments

Value

numeric vector of same length as x with effective mobility values.

Author(s)

Liesa Salzer

Examples

rtime <- c(10,20,30,40,50,60,70,80,90,100)
 marker_rt <-  c(20,80)
 mobility <- c(0, 2000)
 convertMtime(rtime, marker_rt, mobility)

Description

correctRindex performs correction of retention indices (RIs) based on reference substances. Even after conversion of RTs to RIs slight deviations might exist. These deviations can be further normalized, if they are linear, by using two metabolites for which the RIs are known (e.g. internal standards).

Usage

correctRindex(x, y)

Arguments

Value

numeric vector of same length than x with corrected retention indices. Values are floating point decimals. If integer values shall be used conversion has to be performed manually.

Author(s)

Michael Witting

Examples

ref <- data.frame(rindex = c(110, 210),
refindex = c(100, 200))
rindex <- c(110, 210)
correctRindex(rindex, ref)

Description

countElements parses strings representing a chemical formula into a named vector of element counts.

Usage

countElements(x)

Arguments

Value

list of integer with the element counts (names being elements).

Author(s)

Michael Witting and Sebastian Gibb

See Also

pasteElements()

Examples

countElements(c("C6H12O6", "C11H12N2O2"))

Description

The fit_lm and adjust_lm functions facilitate linear model-based normalization of abundance matrices. The expected noise in a numeric data matrix can be modeled with a linear regression model using the fit_lm function and the data can subsequently be adjusted using the adjust_lm function (i.e., the modeled noise will be removed from the abundance values). A typical use case would be to remove injection index dependent signal drifts in a LC-MS derived metabolomics data: a linear model of the form y ~ injection_index could be used to model the measured abundances of each feature (each row in a data matrix) as a function of the injection index in which a specific sample was measured during the LC-MS measurement run. The fitted linear regression models can subsequently be used to adjust the abundance matrix by removing these dependencies from the data. This allows to perform signal adjustments as described in (Wehrens et al. 2016).

The two functions are described in more details below:

fit_lm allows to fit a linear regression model (defined with parameter formula) to each row of the numeric data matrix submitted with parameter y. Additional covariates of the linear model defined in formula are expected to be provided as columns in a data.frame supplied via the data parameter.

The linear model is expected to be defined by a formula starting with ⁠y ~ ⁠. To model for example an injection index dependency of values in y a formula y ~ injection_index could be used, with values for the injection index being provided as a column "injection_index" in the data data frame. fit_lm would thus fit this model to each row of y.

Linear models can be fitted either with the standard least squares of lm() by setting method = "lm" (the default), or with the more robust methods from the robustbase package with method = "lmrob".

adjust_lm can be used to adjust abundances in a data matrix y based on linear regression models provided with parameter lm. Parameter lm is expected to be a list of length equal to the number of rows of y, each element being a linear model (i.e., a results from lm or lmrob). Covariates for the model need to be provided as columns in a data.frame provided with parameter data. The number of rows of that data.frame need to match the number of columns of y. The function returns the input matrix y with values in rows adjusted with the linear models provided by lm. No adjustment is performed for rows for which the respective element in lm is NA. See examples below for details or the vignette for more examples, descriptions and information.

Usage

fit_lm(
  formula,
  data,
  y,
  method = c("lm", "lmrob"),
  control = NULL,
  minVals = ceiling(nrow(data) * 0.75),
  model = TRUE,
  ...,
  BPPARAM = SerialParam()
)

adjust_lm(y = matrix(), data = data.frame(), lm = list(), ...)

Arguments

Value

For `fit_lm`: a `list` with linear models (either of type *lm* or
*lmrob*) or length equal to the number of rows of `y`. `NA` is
reported for rows with too few non-missing data points (depending
on parameter `minValues`).
For `adjust_lm`: a numeric matrix (same dimensions as input matrix
`y`) with the values adjusted with the provided linear models.

Author(s)

Johannes Rainer

References

Wehrens R, Hageman JA, van Eeuwijk F, Kooke R, Flood PJ, Wijnker E, Keurentjes JJ, Lommen A, van Eekelen HD, Hall RD Mumm R and de Vos RC. Improved batch correction in untargeted MS-based metabolomics. Metabolomics 2016; 12:88.

Examples

## See also the vignette for more details and examples.

## Load a test matrix with abundances of features from a LC-MS experiment.
vals <- read.table(system.file("txt", "feature_values.txt",
                                package = "MetaboCoreUtils"), sep = "\t")
vals <- as.matrix(vals)

## Define a data.frame with the covariates to be used to model the noise
sdata <- data.frame(injection_index = seq_len(ncol(vals)))

## Fit a linear model describing the feature abundances as a
## function of the index in which samples were injected during the LC-MS
## run. We're fitting the model to log2 transformed data.
## Note that such a model should **only** be fitted if the samples
## were randomized, i.e. the injection index is independent of any
## experimental covariate. Alternatively, the injection order dependent
## signal drift could be estimated using QC samples (if they were
## repeatedly injected) - see vignette for more details.
ii_lm <- fit_lm(y ~ injection_index, data = sdata, y = log2(vals))

## The result is a list of linear models
ii_lm[[1]]

## Plotting the data for one feature:
plot(x = sdata$injection_index, y = log2(vals[2, ]),
    ylab = expression(log[2]~abundance), xlab = "injection index")
grid()
## plot also the fitted model
abline(ii_lm[[2]], lty = 2)

## For this feature (row) a decreasing signal intensity with injection
## index was observed (and modeled).

## For another feature an increasing intensity can be observed.
plot(x = sdata$injection_index, y = log2(vals[3, ]),
    ylab = expression(log[2]~abundance), xlab = "injection index")
grid()
## plot also the fitted model
abline(ii_lm[[3]], lty = 2)

## This trend can be removed from the data using the `adjust_lm` function
## by providing the linear models descring the drift. Note that, because
## we're adjusting log2 transformed data, the resulting abundances are
## also in log2 scale.
vals_adj <- adjust_lm(log2(vals), data = sdata, lm = ii_lm)

## Plotting the data before (open circles) and after adjustment (filled
## points)
plot(x = sdata$injection_index, y = log2(vals[2, ]),
    ylab = expression(log[2]~abundance), xlab = "injection index")
points(x = sdata$injection_index, y = vals_adj[2, ], pch = 16)
grid()
## Adding the line fitted through the raw data
abline(ii_lm[[2]], lty = 2)
## Adding a line fitted through the adjusted data
abline(lm(vals_adj[2, ] ~ sdata$injection_index), lty = 1)
## After adjustment there is no more dependency on injection index.

Description

formula2mz calculates the m/z values from a list of molecular formulas and adduct definitions.

Custom adduct definitions can be passed to the adduct parameter in form of a data.frame. This data.frame is expected to have columns "mass_add" and "mass_multi" defining the additive and multiplicative part of the calculation. See adducts() for examples.

Usage

formula2mz(formula, adduct = "[M+H]+", standardize = TRUE)

Arguments

Value

Numeric matrix with same number of rows than elements in formula and number of columns being equal to the length of adduct (adduct names are used as column names). Each column thus represents the m/z of formula for each defined adduct.

Author(s)

Roger Gine

Examples

## Calculate m/z values of adducts of a list of formulas
formulas <- c("C6H12O6", "C9H11NO3", "C16H13ClN2O")
ads <- c("[M+H]+", "[M+Na]+", "[2M+H]+", "[M]+")
formula2mz(formulas, ads)
formula2mz(formulas, adductNames()) #All available adducts

## Use custom-defined adducts as input
custom_ads <- data.frame(mass_add = c(1, 2, 3), mass_multi = c(1, 2, 0.5))
formula2mz(formulas, custom_ads)

## Use standardize = FALSE to keep formula unaltered
formula2mz("H12C6O6")
formula2mz("H12C6O6", standardize = FALSE)

Description

indexRtime uses a list of known substances to convert retention times (RTs) to retention indices (RIs). By this retention information is normalized for differences in experimental settings, such as gradient delay volume, dead volume or flow rate. By default linear interpolation is performed, other ways of calculation can supplied as function.

Usage

indexRtime(x, y, FUN = rtiLinear, ...)

Arguments

Value

numeric vector of same length as x with retention indices. Values floating point decimals. If integer values shall be used conversion has to be performed manually

Author(s)

Michael Witting

Examples

rti <- data.frame(rtime = c(1,2,3),
rindex = c(100,200,300))
rtime <- c(1.5, 2.5)
indexRtime(rtime, rti)

Description

internalStandardMixNames returns available names of internal standard mixes provided by the MetaboCoreUtils package.

Usage

internalStandardMixNames()

Value

character names of available IS mixes

Author(s)

Michael Witting

Examples

internalStandardMixNames()

Description

internalStandards returns a table with metabolite standards available in commercial internal standard mixes. The returned data frame contains the following columns:

• "name": the name of the standard

• "formula_salt": chemical formula of the salt that was used to produce the standard mix

• "formula_metabolite": chemical formula of the metabolite in free form

• "smiles_salt": SMILES of the salt that was used to produced the standard mix

• "smiles_metabolite": SMILES of the metabolite in free form

• "mol_weight_salt": molecular (average) weight of the salt (can be used for calculation of molar concentration, etc.)

• "exact_mass_metabolite": exact mass of free metabolites

• "conc": concentration of the metabolite in ug/mL (of salt form)

• "mix": name of internal standard mix

Usage

internalStandards(mix = "QReSS")

Arguments

Value

data.frame data on internal standards

Author(s)

Michael Witting

See Also

internalStandardMixNames() for provided internal standard mixes.

Examples

internalStandards(mix = "QReSS")
internalStandards(mix = "UltimateSplashOne")

Description

In order to identify potential isotopologues based on only m/z and intensity values with the isotopologues() function, sets of pre-calculated parameters are required. This function returns such parameter sets estimated on different sources/databases. The nomenclature used to describe isotopes follows the following convention: the number of neutrons is provided in [ as a prefix to the element and the number of atoms of the element as suffix. ⁠[13]C2[37]Cl3⁠ describes thus an isotopic substitution containing 2 ⁠[13]C⁠ isotopes and 3 ⁠[37]Cl⁠ isotopes.

Each row in the returned data.frame is associated with an isotopic substitution (which can involve isotopes of several elements or different isotopes of the same element). In general for each isotopic substitution multiple rows are present in the data.frame. Each row provides parameters to compute bounds (for the ratio between the isotopologue peak and the monoisotopic one) on a certain mass range. The provided isotopic substitutions are in general the most frequently observed substitutions in the database (e.g. HMDB) on which they were defined. Parameters (columns) defined for each isotopic substitution are:

• "minmass": the minimal mass of a compound for which the isotopic substitution was found. Peaks with a mass lower than this will most likely not have the respective isotopic substitution.

• "maxmass": the maximal mass of a compound for which the isotopic substitution was found. Peaks with a mass higher than this will most likely not have the respective isotopic substitution.

• "md": the mass difference between the monoisotopic peak and a peak of an isotopologue characterized by the respective isotopic substitution.

• "leftend": left endpoint of the mass interval.

• "rightend": right endpoint of the mass interval.

• "LBint": intercept of the lower bound line on the mass interval whose endpoints are "leftend" and "rightend".

• "LBslope": slope of the lower bound line on the mass interval.

• "UBint": intercept of the upper bound line on the mass interval.

• "UBslope": slope of the upper bound line on the mass interval.

Usage

isotopicSubstitutionMatrix(source = c("HMDB_NEUTRAL"))

Arguments

Value

data.frame with parameters to detect the defined isotopic substitutions

Available pre-calculated substitution matrices

• source = "HMDB": most common isotopic substitutions and parameters for these have been calculated for all compounds from the Human Metabolome Database (HMDB, July 2021). Note that the substitutions were calculated on the neutral masses (i.e. the chemical formulas of the compounds, not considering any adducts).

Author(s)

Andrea Vicini

Examples

## Get the substitution matrix calculated on HMDB
isotopicSubstitutionMatrix("HMDB_NEUTRAL")

Description

Given a spectrum (i.e. a peak matrix with m/z and intensity values) the function identifies groups of potential isotopologue peaks based on pre-defined mass differences and intensity (probability) ratios that need to be passed to the function with the substDefinition parameter. Each isotopic substitution in a compound determines a certain isotopologue and it is associated with a certain mass difference of that with respect to the monoisotopic isotopologue. Also each substitution in a compound is linked to a certain ratio between the intensities of the peaks of the corresponding isotopologue and the monoisotopic one. This ratio isn't the same for isotopologues corresponding to the same isotopic substitution but to different compounds. Through the substDefinition parameter we provide upper and lower values to compute bounds for each isotopic substitution dependent on the peak's mass.

Usage

isotopologues(
  x,
  substDefinition = isotopicSubstitutionMatrix(),
  tolerance = 0,
  ppm = 20,
  seedMz = numeric(),
  charge = 1,
  .check = TRUE
)

Arguments

Details

The function iterates over the peaks (rows) in x. For each peak (which is assumed to be the monoisotopic peak) it searches other peaks in x with a difference in mass matching (given ppm and tolerance) any of the pre-defined mass differences in substDefinitions (column "md"). The mass is obtained by multiplying the m/z of the peaks for the charge expected for the ionized compounds.

For matching peaks, the function next evaluates whether their intensity is within the expected (pre-defined) intensity range. Using "LBint", "LBslope", "UBint", "UBslope" of the previously matched isotopic substitution in substDefinition, the function estimates a (mass dependent) lower and upper intensity ratio limit based on the peak's mass.

When some peaks are grouped together their indexes are excluded from the set of indexes that are searched for further groups (i.e. peaks already assigned to an isotopologue group are not considered/tested again thus each peak can only be part of one isotopologue group).

Value

list of integer vectors. Each integer vector contains the indixes of the rows in x with potential isotopologues of the same compound.

Author(s)

Andrea Vicini

Examples

## Read theoretical isotope pattern (high resolution) from example file
x <- read.table(system.file("exampleSpectra",
    "serine-alpha-lactose-caffeine.txt", package = "MetaboCoreUtils"),
    header = TRUE)
x <- x[order(x$mz), ]
plot(x$mz, x$intensity, type = "h")

isos <- isotopologues(x, ppm = 5)
isos

## highlight them in the plot
for (i in seq_along(isos)) {
    z <- isos[[i]]
    points(x$mz[z], x$intensity[z], col = i + 1)
}

Description

mass2mz calculates the m/z value from a neutral mass and an adduct definition.

Custom adduct definitions can be passed to the adduct parameter in form of a data.frame. This data.frame is expected to have columns "mass_add" and "mass_multi" defining the additive and multiplicative part of the calculation. See adducts() for examples.

Usage

mass2mz(x, adduct = "[M+H]+")

Arguments

Value

numeric matrix with same number of rows than elements in x and number of columns being equal to the length of adduct (adduct names are used as column names). Each column thus represents the m/z of x for each defined adduct.

Author(s)

Michael Witting, Johannes Rainer

See Also

mz2mass() for the reverse calculation, adductNames() for supported adduct definitions.

Examples

exact_mass <- c(100, 200, 250)
adduct <- "[M+H]+"

## Calculate m/z of [M+H]+ adduct from neutral mass
mass2mz(exact_mass, adduct)

exact_mass <- 100
adduct <- "[M+Na]+"

## Calculate m/z of [M+Na]+ adduct from neutral mass
mass2mz(exact_mass, adduct)

## Calculate m/z of multiple adducts from neutral mass
mass2mz(exact_mass, adduct = adductNames())

## Provide a custom adduct definition.
adds <- data.frame(mass_add = c(1, 2, 3), mass_multi = c(1, 2, 0.5))
rownames(adds) <- c("a", "b", "c")
mass2mz(c(100, 200), adds)

Description

The mclosest function calculates the closest rows between two matrices (or data frames) considering pairwise differences between values in columns of x and table. It returns the index of the closest row in table for each row in x.

Usage

mclosest(x, table, ppm = 0, tolerance = Inf)

Arguments

Details

If, for a row of x, two rows of table are closest only the index of first row will be returned.

For both the tolerance and ppm arguments, if their length is different to the number of columns of x and table, the input argument will be replicated to match it.

Value

integer vector of indices indicating the closest row of table for each row of x. If no suitable match is found for a row in x based on the specified tolerance and ppm, the corresponding index is set to NA.

Author(s)

Philippine Louail

Examples

x <- data.frame(a = 1:5, b = 3:7)
table <- data.frame(c = c(11, 23, 3, 5, 1), d = c(32:35, 45))

## Get for each row of `x` the index of the row in `table` with the smallest
## difference of values (per column)
mclosest(x, table)

## If the absolute difference is larger than `tolerance`, return `NA`. Note
## that the tolerance value of `25` is used for difference for each pairwise
## column in `x` and `table`.
mclosest(x, table, tolerance = 25)

Description

multiplyElements Multiply the number of atoms of each element by a constant, positive, integer

Usage

multiplyElements(x, k)

Arguments

Value

character strings with the standardized chemical formula.

Author(s)

Roger Gine

Examples

multiplyElements("H2O", 3)

multiplyElements(c("C6H12O6", "Na", "CH4O"), 2)

Description

mz2mass calculates the neutral mass from a given m/z value and adduct definition.

Custom adduct definitions can be passed to the adduct parameter in form of a data.frame. This data.frame is expected to have columns "mass_add" and "mass_multi" defining the additive and multiplicative part of the calculation. See adducts() for examples.

Usage

mz2mass(x, adduct = "[M+H]+")

Arguments

Value

numeric matrix with same number of rows than elements in x and number of columns being equal to the length of adduct (adduct names are used as column names. Each column thus represents the neutral mass of x for each defined adduct.

Author(s)

Michael Witting, Johannes Rainer

See Also

mass2mz() for the reverse calculation, adductNames() for supported adduct definitions.

Examples

ion_mass <- c(100, 200, 300)
adduct <- "[M+H]+"

## Calculate m/z of [M+H]+ adduct from neutral mass
mz2mass(ion_mass, adduct)

ion_mass <- 100
adduct <- "[M+Na]+"

## Calculate m/z of [M+Na]+ adduct from neutral mass
mz2mass(ion_mass, adduct)

## Provide a custom adduct definition.
adds <- data.frame(mass_add = c(1, 2, 3), mass_multi = c(1, 2, 0.5))
rownames(adds) <- c("a", "b", "c")
mz2mass(c(100, 200), adds)

Description

pasteElements creates a chemical formula from element counts (such as returned by countElements()).

Usage

pasteElements(x)

Arguments

Value

character() with the chemical formulas.

Author(s)

Michael Witting and Sebastian Gibb

See Also

countElements()

Examples

elements <- c("C" = 6, "H" = 12, "O" = 6)
pasteElements(elements)

Description

The following functions allow to calculate basic quality assessment estimates typically employed in the analysis of metabolomics data. These functions are designed to be applied to entire rows of data, where each row corresponds to a feature. Subsequently, these estimates can serve as a foundation for feature filtering.

• rsd and rowRsd are convenience functions to calculate the relative standard deviation (i.e. coefficient of variation) of a numerical vector or for rows of a numerical matrix, respectively.

• rowDratio computes the D-ratio or dispersion ratio, defined as the standard deviation for QC (Quality Control) samples divided by the standard deviation for biological test samples, for each feature (row) in the matrix.

• percentMissing and rowPercentMissing determine the percentage of missing values in a vector or for each row of a matrix, respectively.

• rowBlank identifies rows (i.e., features) where the mean of test samples is lower than a specified multiple (defined by the threshold parameter) of the mean of blank samples. This can be used to flag features that result from contamination in the solvent of the samples.

These functions are based on standard filtering methods described in the literature, and they are implemented to assist in preprocessing metabolomics data.

Usage

rsd(x, na.rm = TRUE, mad = FALSE)

rowRsd(x, na.rm = TRUE, mad = FALSE)

rowDratio(x, y, na.rm = TRUE, mad = FALSE)

percentMissing(x)

rowPercentMissing(x)

rowBlank(x, y, threshold = 2, na.rm = TRUE)

Arguments

Value

See individual function description above for details.

Note

For rsd and rowRsd the feature abundances are expected to be provided in natural scale and not e.g. log2 scale as it may lead to incorrect interpretations.

Author(s)

Philippine Louail, Johannes Rainer

References

Broadhurst D, Goodacre R, Reinke SN, Kuligowski J, Wilson ID, Lewis MR, Dunn WB. Guidelines and considerations for the use of system suitability and quality control samples in mass spectrometry assays applied in untargeted clinical metabolomic studies. Metabolomics. 2018;14(6):72. doi: 10.1007/s11306-018-1367-3. Epub 2018 May 18. PMID: 29805336; PMCID: PMC5960010.

Examples

## coefficient of variation
a <- c(4.3, 4.5, 3.6, 5.3)
rsd(a)

A <- rbind(a, a, a)
rowRsd(A)

## Dratio
x <- c(4.3, 4.5, 3.6, 5.3)
X <- rbind(a, a, a)
rowDratio(X, X)

#' ## Percent Missing
b <- c(1, NA, 3, 4, NA)
percentMissing(b)

B <- matrix(c(1, 2, 3, NA, 5, 6, 7, 8, 9), nrow = 3)
rowPercentMissing(B)

## Blank Rows
test_samples <- matrix(c(13, 21, 3, 4, 5, 6), nrow = 2)
blank_samples <- matrix(c(0, 1, 2, 3, 4, 5), nrow = 2)
rowBlank(test_samples, blank_samples)

Description

standardizeFormula standardizes a supplied chemical formula according to the Hill notation system.

Usage

standardizeFormula(x)

Arguments

Value

character strings with the standardized chemical formula.

Author(s)

Michael Witting and Sebastian Gibb

See Also

pasteElements() countElements()

Examples

standardizeFormula("C6O6H12")

Description

subtractElements subtracts one chemical formula from another.

Usage

subtractElements(x, y)

Arguments

Value

character Resulting formula

Author(s)

Michael Witting and Sebastian Gibb

Examples

subtractElements("C6H12O6", "H2O")

subtractElements("C6H12O6", "NH3")