从 R data.table 中的每一列中减去每一列 [英] Subtract every column from each other column in a R data.table

问题描述

假设我有一个 data.table

Let's say I have a data.table

set.seed(1) # to make the example reproducible
ex<-data.table(AAA=runif(100000),
               BBB=runif(100000),
               CCC=runif(100000),
               DDD=runif(100000),
               FLAG=c(rep(c("a","b","c","d","e"),200000)))

我想从列 AAA 中减去每隔一列，然后从 BBB 中减去每个剩余的列(FLAG 除外)，依此类推，以使输出看起来像...

I want to subtract from column AAA every other column, then from BBB every remaining column (except FLAG) and so on so that the output will look like...

ex[,list(AAA_BBB=AAA-BBB,
         AAA_CCC=AAA-CCC,
         AAA_DDD=AAA-DDD,
         BBB_CCC=BBB-CCC,
         BBB_DDD=BBB-DDD,
         CCC_DDD=CCC-DDD)]

是否有一个 data.table 语法可以在不知道有多少列或它们的名称是什么的情况下干净地做到这一点?

Is there a data.table syntax that can do this cleanly without knowing how many columns there are or what their names are?

推荐答案

循环遍历data.table中的组合:

Looping over the combinations within data.table:

comblist <- combn(names(ex)[-5],2,FUN=list)
res2 <- ex[,lapply(comblist,function(x) get(x[1])-get(x[2]))]

setnames(res2,names(res2),sapply(comblist,paste,collapse="_"))

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