从数据框中的前 2 个元素创建一个字符串并添加到 R 中的新列

Question

I think this is fairly simple, say I have a data frame

> vadata 
    va1 va2
1   a   c
2   b   d

I want to create a new column va3 = "ac" and "bd" for all rows in vadata and append to vadata?

vadata is of type dataframe.

Is there an easy to way do this in r?

Answer 1

你可以使用paste来做到这一点。

vadata$va3 <- paste(vadata$va1,vadata$va2,sep="-")

Answer 2

You can use the mutate() from dplyr library.

library(dplyr)
vadata = vadata %>% mutate(va3 = paste(va1,va2, sep='-'))
vadata

  va1 va2 va3
1   a   c a-c
2   b   d b-d

Using mutate(), at a time you can create multiple columns. For example:

vadata = vadata %>% mutate(va3 = paste(va1,va2, sep='-'),
                           va4 = paste(va3,va2, sep='-))

Answer 3

You can try the following base R code, which applies to any number of columns

vadataout <- cbind(vadata,matrix(paste(vadata[,1],as.matrix(vadata[-1]),sep = "-"),nrow = nrow(vadata)))

Example

vadata <- data.frame(matrix(1:60,nrow = 2))

> vadata
  X1 X2 X3 X4 X5 X6 X7 X8 X9 X10 X11 X12 X13 X14 X15 X16 X17 X18 X19 X20 X21 X22 X23 X24 X25 X26 X27 X28 X29 X30
1  1  3  5  7  9 11 13 15 17  19  21  23  25  27  29  31  33  35  37  39  41  43  45  47  49  51  53  55  57  59
2  2  4  6  8 10 12 14 16 18  20  22  24  26  28  30  32  34  36  38  40  42  44  46  48  50  52  54  56  58  60

and you will get

> vadataout
  X1 X2 X3 X4 X5 X6 X7 X8 X9 X10 X11 X12 X13 X14 X15 X16 X17 X18 X19 X20 X21 X22 X23 X24 X25 X26 X27 X28 X29 X30   1   2   3    4    5    6    7
1  1  3  5  7  9 11 13 15 17  19  21  23  25  27  29  31  33  35  37  39  41  43  45  47  49  51  53  55  57  59 1-3 1-5 1-7  1-9 1-11 1-13 1-15
2  2  4  6  8 10 12 14 16 18  20  22  24  26  28  30  32  34  36  38  40  42  44  46  48  50  52  54  56  58  60 2-4 2-6 2-8 2-10 2-12 2-14 2-16
     8    9   10   11   12   13   14   15   16   17   18   19   20   21   22   23   24   25   26   27   28   29
1 1-17 1-19 1-21 1-23 1-25 1-27 1-29 1-31 1-33 1-35 1-37 1-39 1-41 1-43 1-45 1-47 1-49 1-51 1-53 1-55 1-57 1-59
2 2-18 2-20 2-22 2-24 2-26 2-28 2-30 2-32 2-34 2-36 2-38 2-40 2-42 2-44 2-46 2-48 2-50 2-52 2-54 2-56 2-58 2-60

Answer 4

因为我正在做 35 个类别，所以我发现遍历每一行 nrow() 的 for 循环是最简单和最简单的解决方案，并且适用于基础 R。