Package 'lefser'

Identify which elements of a string are terminal nodes

Description

A terminal node in a taxonomy does not have any child nodes. For example, a species is a terminal node if there are no subspecies or strains that belong to that species. This function identifies which elements of a vector are terminal nodes simply by checking whether that element appears as a substring in any other element of the vector.

Usage

get_terminal_nodes(string)

Arguments

string

A character vector of strings to check for terminal nodes

Value

A logical vector indicating which elements of the string are terminal nodes

Examples

# What does it do?
data("zeller14")
rownames(zeller14)[988:989]
get_terminal_nodes(rownames(zeller14)[988:989])
# How do I use it to keep only terminal nodes for a lefser analysis?
terminal_nodes <- get_terminal_nodes(rownames(zeller14))
zeller14sub <- zeller14[terminal_nodes, ]
# Then continue with your analysis!

---

R implementation of the LEfSe method

Description

Perform a LEfSe analysis: the function carries out differential analysis between two sample groups for multiple features and uses linear discriminant analysis to establish their effect sizes. Subclass information for each class can be incorporated into the analysis (see examples). Features with large differences between two sample groups are identified as biomarkers.

Usage

lefser(
  relab,
  kruskal.threshold = 0.05,
  wilcox.threshold = 0.05,
  lda.threshold = 2,
  groupCol = "GROUP",
  blockCol = NULL,
  assay = 1L,
  trim.names = FALSE,
  checkAbundances = TRUE,
  method = "none",
  ...,
  expr
)

Arguments

relab	A SummarizedExperiment with relative abundances in the assay
kruskal.threshold	numeric(1) The p-value for the Kruskal-Wallis Rank Sum Test (default 0.05). If multiple hypothesis testing is performed, this threshold is applied to corrected p-values.
wilcox.threshold	numeric(1) The p-value for the Wilcoxon Rank-Sum Test when 'blockCol' is present (default 0.05). If multiple hypothesis testing is performed, this threshold is applied to corrected p-values.
lda.threshold	numeric(1) The effect size threshold (default 2.0).
groupCol	character(1) Column name in colData(relab) indicating groups, usually a factor with two levels (e.g., c("cases", "controls"); default "GROUP").
blockCol	character(1) Optional column name in colData(relab) indicating the blocks, usually a factor with two levels (e.g., c("adult", "senior"); default NULL).
assay	The i-th assay matrix in the SummarizedExperiment ('relab'; default 1).
trim.names	Default is FALSE. If TRUE, this function extracts the most specific taxonomic rank of organism.
checkAbundances	logical(1) Whether to check if the assay data in the relab input are relative abundances or counts. If counts are found, a warning will be emitted (default TRUE).
method	Default is "none" as in the original LEfSe implementation. Character string of length one, passed on to p.adjust to set option for multiple testing. For multiple pairwise comparisons, each comparison is adjusted separately. Options are "holm", "hochberg", "hommel", "bonferroni", "BH", "BY", "fdr" (synonym for "BH"), and "none".
expr	(deprecated) Use relab instead. A SummarizedExperiment with relative abundances in the assay
...	Additional inputs to lower level functions (not used).

Details

The LEfSe method expects relative abundances in the expr input. A warning will be emitted if the column sums do not result in 1. Use the relativeAb helper function to convert the data in the SummarizedExperiment to relative abundances. The checkAbundances argument enables checking the data for presence of relative abundances and can be turned off by setting the argument to FALSE.

Value

The function returns a data.frame with two columns, which are names of features and their LDA scores.

Examples

data(zeller14)
    zeller14 <- zeller14[, zeller14$study_condition != "adenoma"]
    tn <- get_terminal_nodes(rownames(zeller14))
    zeller14tn <- zeller14[tn,]
    zeller14tn_ra <- relativeAb(zeller14tn)
    
    # (1) Using classes only
    res_group <- lefser(zeller14tn_ra, 
                        groupCol = "study_condition")
    # (2) Using classes and sub-classes
    res_block <- lefser(zeller14tn_ra, 
                        groupCol = "study_condition", 
                        blockCol = "age_category")

---

Plots results from lefser function

Description

This function plots the biomarkers found by LEfSe, that are ranked according to their effect sizes and linked to their abundance in each class.

Usage

lefserPlot(
  df,
  colors = c("red", "forestgreen"),
  trim.names = TRUE,
  title = "",
  label.font.size = 3
)

Arguments

df	Data frame produced by lefser.
colors	A character(2). Colors corresponding to class 0 and 1. Defaults to c("red", "forestgreen").
trim.names	Under the default (TRUE), this function extracts the most specific taxonomic rank of organism.
title	A character(1). The title of the plot.
label.font.size	A numeric(1). The font size of the feature labels. The default is 3.

Value

Function returns plot of effect size scores produced by lefser. Positive scores represent the biomarker is more abundant in class '1'. Negative scores represent the biomarker is more abundant in class '0'.

Examples

example("lefser")
lefserPlot(res_group)

---

Utility function to calculate relative abundances

Description

The function calculates the column totals and divides each value within the column by the respective column total.

This function calculates the relative abundance of each feature in the SummarizedExperiment object containing count data, expressed as counts per million (CPM)

Usage

relativeAb(se, assay = 1L)

Arguments

se	A SummarizedExperiment object with counts
assay	The i-th assay matrix in the SummarizedExperiment ('relab'; default 1).

Value

returns a new SummarizedExperiment object with counts per million calculated and added as a new assay named rel_abs.

Examples

se <- SummarizedExperiment(
    assays = list(
        counts = matrix(
            rep(1, 4), ncol = 1, dimnames = list(LETTERS[1:4], "SAMP")
        )
    )
)
assay(se)
assay(relativeAb(se))

---

Example dataset for lefser

Description

The ZellerG_2014 dataset contains microbiome count data for CRC patients and controls. It was for curatedMetagenomicData using the script in the package directory "data-raw".

Usage

data("zeller14")

Format

A SummarizedExperiment with 1585 features, 199 samples

study_condition

adenoma, control, CRC

age_category

adult, senior

Source

https://pubmed.ncbi.nlm.nih.gov/25432777/

---