# pairwiseFC: Compute pairwise fold changes In stamats/MKmisc: Miscellaneous Functions from M. Kohl

## Description

This function computes pairwise fold changes. It also works for logarithmic data.

## Usage

 `1` ```pairwise.fc(x, g, ave = mean, log = TRUE, base = 2, mod.fc = TRUE, ...) ```

## Arguments

 `x` numeric vector. `g` grouping vector or factor `ave` function to compute the group averages. `log` logical. Is the data logarithmic? `base` If `log = TRUE`, the base which was used to compute the logarithms. `mod.fc` logical. Return modified fold changes? (see details) `...` optional arguments to `ave`.

## Details

The function computes pairwise fold changes between groups, where the group values are aggregated using the function which is given by the argument `ave`.

The fold changes are returned in a slightly modified form if mod.fc = TRUE. Fold changes `FC` which are smaller than `1` are reported as to `-1/FC`.

The implementation is in certain aspects analogously to `pairwise.t.test`.

## Value

Vector with pairwise fold changes.

## Author(s)

Matthias Kohl [email protected]

`pairwise.t.test`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14``` ```set.seed(13) x <- rnorm(100) ## assumed as log2-data g <- factor(sample(1:4, 100, replace = TRUE)) levels(g) <- c("a", "b", "c", "d") pairwise.fc(x, g) ## some small checks res <- by(x, list(g), mean) 2^(res[[1]] - res[[2]]) # a vs. b -1/2^(res[[1]] - res[[3]]) # a vs. c 2^(res[[1]] - res[[4]]) # a vs. d -1/2^(res[[2]] - res[[3]]) # b vs. c -1/2^(res[[2]] - res[[4]]) # b vs. d 2^(res[[3]] - res[[4]]) # c vs. d ```