理解`Reduce`功能 [英] Understand the `Reduce` function

问题描述

我有一个关于 R 中的 Reduce 函数的问题.我阅读了它的文档，但我仍然有点困惑.所以，我有 5 个带有基因名称的向量.例如:

I have a question about the Reduce function in R. I read its documentation, but I am still confused a bit. So, I have 5 vectors with genes name. For example:

v1 <- c("geneA","geneB",""...)
v2 <- c("geneA","geneC",""...)
v3 <- c("geneD","geneE",""...)
v4 <- c("geneA","geneE",""...)
v5 <- c("geneB","geneC",""...)

我想找出至少两个载体中存在哪些基因.有人建议:

And I would like to find out which genes are present in at least two vectors. Some people have suggested:

Reduce(intersect,list(a,b,c,d,e))

如果有人能向我解释这个语句是如何工作的，我将不胜感激，因为我已经看到 Reduce 用于其他场景.

I would greatly appreciate if someone could please explain to me how this statement works, because I have seen Reduce used in other scenarios.

推荐答案

Reduce 接受一个二元函数和一个数据项列表，并以递归方式连续将该函数应用于列表元素.例如:

Reduce takes a binary function and a list of data items and successively applies the function to the list elements in a recursive fashion. For example:

Reduce(intersect,list(a,b,c))

与

intersect((intersect(a,b),c)

但是，我认为该构造不会在这里帮助您，因为它只会返回那些对所有向量通用的元素.

However, I don't think that construct will help you here as it will only return those elements that are common to all vectors.

要计算基因出现在其中的载体数量，您可以执行以下操作:

To count the number of vectors that a gene appears in you could do the following:

vlist <- list(v1,v2,v3,v4,v5)
addmargins(table(gene=unlist(vlist), vec=rep(paste0("v",1:5),times=sapply(vlist,length))),2,list(Count=function(x) sum(x[x>0])))
       vec
gene    v1 v2 v3 v4 v5 Count
  geneA  1  1  0  1  0     3
  geneB  1  0  0  0  1     2
  geneC  0  1  0  0  1     2
  geneD  0  0  1  0  0     1
  geneE  0  0  1  1  0     2

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