如何对两个ffdf进行列绑定 [英] How to column bind two ffdf

问题描述

假设有两个ffdf文件:

library(ff)
ff1 <- as.ffdf(data.frame(matrix(rnorm(10*10),ncol=10)))
ff2 <- ff1
colnames(ff2) <- 1:10

如何在不将它们加载到内存的情况下对它们进行列绑定? cbind不起作用.

How can I column bind these without loading them into memory? cbind doesn't work.

有相同的问题http://stackoverflow.com/questions/18355686/columnbind-ff-data-frames-in-r，但没有MWE，作者放弃了，所以我重新发布了.

There is the same question http://stackoverflow.com/questions/18355686/columnbind-ff-data-frames-in-r but it does not have an MWE and the author abandoned it so I reposted.

推荐答案

您可以使用以下构造cbind.ffdf2，确保两个输入ffdf的列名不重复:

You can use the following construct cbind.ffdf2, making sure the column names of the two input ffdf's are not duplicate:

library(ff)
ff1 <- as.ffdf(data.frame(letA = letters[1:5], numA = 1:5))
ff2 <- as.ffdf(data.frame(letB = letters[6:10], numB = 6:10))

cbind.ffdf2 <- function(d1, d2){
  D1names <- colnames(d1)
  D2names <- colnames(d2)
  mergeCall <- do.call("ffdf", c(physical(d1), physical(d2)))
  colnames(mergeCall) <- c(D1names, D2names)
  mergeCall
}

cbind.ffdf2(ff1, ff2)[,]

结果:

   letA numA letB numB
1   a    1    f     6
2   b    2    g     7
3   c    3    h     8
4   d    4    i     9
5   e    5    j    10

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