R:合并大数据框 [英] R: coalescing a large data frame

问题描述

假设我创建了一个数据框，foo:

Say I create a data frame, foo:

foo <- data.frame(A=rep(NA,10),B=rep(NA,10))
foo$A[1:3] <- "A"
foo$B[6:10] <- "B"

看起来像，

      A    B
1     A <NA>
2     A <NA>
3     A <NA>
4  <NA> <NA>
5  <NA> <NA>
6  <NA>    B
7  <NA>    B
8  <NA>    B
9  <NA>    B
10 <NA>    B

我可以coalesce把它合并成一列，就像这样:

I can coalesce this into a single column, like this:

data.frame(AB = coalesce(foo$A, foo$B))

给予，

     AB
1     A
2     A
3     A
4  <NA>
5  <NA>
6     B
7     B
8     B
9     B
10    B

这很好.现在，假设我的数据框很大，有很多列.我如何coalesce 而不单独命名每一列?据我了解，coalesce 期待向量，所以我没有看到一个整洁的 dplyr 解决方案，我可以在其中取出所需的列并将它们传递给 en大众.有什么想法吗?

which is nice. Now, say my data frame is huge with lots of columns. How do I coalesce that without naming each column individually? As far as I understand, coalesce is expecting vectors, so I don't see a neat and tidy dplyr solution where I can just pluck out the required columns and pass them en masse. Any ideas?

编辑

根据要求，一个更难"的例子.

As requested, a "harder" example.

foo <- data.frame(A=rep(NA,10),B=rep(NA,10),C=rep(NA,10),D=rep(NA,10),E=rep(NA,10),F=rep(NA,10),G=rep(NA,10),H=rep(NA,10),I=rep(NA,10),J=rep(NA,10))
foo$A[1] <- "A"
foo$B[2] <- "B"
foo$C[3] <- "C"
foo$D[4] <- "D"
foo$E[5] <- "E"
foo$F[6] <- "F"
foo$G[7] <- "G"
foo$H[8] <- "H"
foo$I[9] <- "I"
foo$J[10] <- "J"

如何在无需编写的情况下合并:

How do I coalesce this without having to write:

data.frame(ALL= coalesce(foo$A, foo$B, foo$C, foo$D, foo$E, foo$F, foo$G, foo$H, foo$I, foo$J))

推荐答案

您可以使用 do.call(coalesce, ...)，这是一种更简单的方法来编写带有很多论点:

You can use do.call(coalesce, ...), which is a simpler way to write a function call with a lot of arguments:

library(dplyr)
do.call(coalesce, foo)
# [1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J"

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