How to multiply a column in a list by a constant in R

user_3225661 0
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I have done a PCA of a tibble df and I have obtained the list res.pca as a result.

I want to multiply the column CP2 in res.pca$rotation and in res.pca$x by -1.

I don't know how to multiply a constant by an element of a list.

library(tidyverse)

set.seed <- 1234
df <- tibble(a = runif(10),
             b = runif(10),
             c = runif(10),
             d = runif(10),
             e = runif(10),
             f = runif(10))

res.pca <- prcomp(df, scale = TRUE)

# How to multiply column PC2 by -1 ?
res.pca$rotation
#>           PC1         PC2         PC3         PC4         PC5        PC6
#> a -0.53522848  0.01623546 -0.17683875  0.53424822 -0.57591012  0.2547574
#> b  0.09345152 -0.10070446 -0.97591986 -0.09645054  0.06631633 -0.1224961
#> c -0.60060502  0.19351430  0.03334125 -0.04015348  0.18352003 -0.7519457
#> d -0.35361738  0.60631081 -0.11196246 -0.27535181  0.36203644  0.5365793
#> e  0.34230164  0.42828520 -0.04659627  0.74868543  0.34975861 -0.1198716
#> f  0.31914768  0.63332948 -0.02213681 -0.25945200 -0.61387997 -0.2288767
res.pca$x
#>              PC1        PC2         PC3        PC4         PC5         PC6
#>  [1,] -0.6358524  0.5828874 -1.38893192  0.8278318  0.45765671  0.36713422
#>  [2,]  0.2867744  0.9462777 -0.02085629 -0.1507573  0.07456675 -0.85216056
#>  [3,]  2.5912151 -1.3097803 -0.68040264  0.1440942  0.30874470  0.04728797
#>  [4,] -0.9248741 -2.0135367 -0.46770160 -0.5386261 -0.08233173 -0.24589384
#>  [5,] -1.7083258  0.1834963  0.32759227  1.0044239  0.49562619 -0.11892058
#>  [6,]  0.4594589  2.1631258  0.32585525  0.4079981 -0.46661003  0.08308276
#>  [7,] -1.5698588  0.6305786 -1.05203941 -1.6090313 -0.26425202  0.21223261
#>  [8,] -1.2245220 -0.6453317  2.13533845 -0.3398981  0.22386580  0.23298046
#>  [9,]  0.2014890 -1.0794984  0.10611970  1.0145475 -0.94717249  0.08065278
#> [10,]  2.5244957  0.5417812  0.71502618 -0.7605828  0.19990613  0.19360418
Created on 2021-07-13 by the reprex package (v2.0.0)
r list
1 Answers

Use lapply to loop over the extracted list elements 'rotation', 'x', get the 'PC2' (matrix), multiply by -1, and return the element i.e. x (lambda function)

res.pca[c("rotation", "x")] <- lapply(res.pca[c("rotation", "x")], 
         function(x) {x[, "PC2"] <- x[, "PC2"] * -1
        x})
user_37322710
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