添加基于另一列 R data.table 的列 [英] Adding a column based on another column R data.table

问题描述

我在 R 中有两个数据表:

I have two data tables in R:

#install.packages("data.table")
library(data.table)
dt1 <- data.table(Num = c(1,1,1,2,2,2,2,3,3,3,3,3,3,4,4,4,4,4,4,4,5,5,5))
dt2 <- data.table(Num = 1:5, Letter = c('A','B','C','D','E'))

我想在第一个基于dt2的数据表中添加一列，所以它将有两列:

I want to add a column to the first data table based on dt2, so it will have two columns:

dt1 <- dt1[,Letter := "THIS WILL CONTAIN AN 'A' FOR EVERY '1', 'B' FOR EVERY '2', ETC"]

第二个数据表作为键，哪个字母对应另一个数据表中的哪个数字.

The second data table serves as a key for which letter corresponds to which number in another data table.

谢谢.

推荐答案

setkey(dt1, Num)
setkey(dt2, Num)
dt2[dt1]
    Num Letter
 1:   1      A
 2:   1      A
 3:   1      A
 4:   2      B
 5:   2      B

这篇关于添加基于另一列 R data.table 的列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！