有条件地用 data.table 替换列值

本文介绍了有条件地用 data.table 替换列值的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我有以下data.table:

I have the following data.table:

dt <- data.table(col1 = rep("a",6), col2 = c(1,1,1,2,3,1))

现在我想用值bigDog"替换 col2 中的所有 1.我可以使用 data.frame 精神做到这一点:

Now I want to replace all the 1 in col2 with value "bigDog". I can do it using the data.frame spirit:

dt$col2[dt$col2==1,] <- "bigDog"

但我想知道是否有不同的方式，更多面向data.table"?

But I wonder if there is a different way, more "data.table oriented"?

推荐答案

如果你不想改变列的类型，你会这样做:

Had you not wanted to change the type of the column, you'd do:

dt[col2 == 1, col2 := 123]

随着类型的改变，你可以这样做:

With the type change, you can do:

dt[, col2 := as.character(col2)][col2 == "1", col2 := "bigDog"]

如果您不先更改类型，bigDog"将被强制转换为整数，即 NA.当然，您还会收到一堆警告.

If you don't change the type first, "bigDog" will get coerced to integer, i.e. NA. You'll also get a bunch of warnings about that of course.

请注意，除了不那么繁琐的语法之外，使用 := 的优点是不会制作额外的数据副本(如 <- 那样)，而是在原地修改.

Note that besides less cumbersome syntax, using := has the advantage of not making extra copies of data (as <- will) and instead modifies in place.