更好地通过引用indeces来添加data.frame列 [英] Better way of adding data.frame columns by referring to indeces

问题描述

这个问题似乎是基本的，但我无法找到答案。

This question seems basic but I have not been able to find an answer to it.

我想添加一个数据列。

I want to add columns of a data.frame together by just referring to their indeces.

假设我要添加1,2和4列。

Suppose I want to add columns 1,2, and 4.

df <- data.frame(
  a=rep(1, 5),
  b=rep(2, 5),
  c=rep(3, 5),
  d=rep(4, 5)
)

我知道明确地提到可以做的列名称

I know that explicitly referring to the column names I can do

> df$a + df$b + df$d
[1] 7 7 7 7 7

指的是我可以做的事情

> df[1] + df[2] + df[4]
  a
1 7
2 7
3 7
4 7
5 7

但是，上面的索引选项需要我写出数据的名称。

However, the index option above requires me to write out the name of the data.frame for every column I want to add.

有没有办法将这些列添加在一起，而只是引用indeces和 data.frame 一次？

Is there a way to add these columns together while just referring to the indeces and the data.frame once?

推荐答案

可以使用rowSums函数并参考通过在 df [，] 中设置列号向量的列。

You can use the rowSums function and refer to columns by setting a vector of column numbers in df[, ].

rowSums(df[, c(1,2,4)]
[1] 7 7 7 7 7

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