重复向量以填充数据框中的列 [英] Repeat vector to fill down column in data frame

问题描述

似乎这种非常简单的操作曾经为我工作，但现在却没有。问题的虚拟版本：

Seems like this very simple maneuver used to work for me, and now it simply doesn't. A dummy version of the problem:

df <- data.frame(x = 1:5) # create simple dataframe
df
  x
1 1
2 2
3 3
4 4
5 5

df$y <- c(1:5) # adding a new column with a vector of the exact same length. Works out like it should
df
 x y
1 1 1
2 2 2
3 3 3
4 4 4
5 5 5

df$z <- c(1:4) # trying to add a new colum, this time with a vector with less elements than there are rows in the dataframe.

Error in `$<-.data.frame`(`*tmp*`, "z", value = 1:4) : 
  replacement has 4 rows, data has 5

我期望它能产生以下结果：

I was expecting this to work with the following result:

 x y z
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4
5 5 5 1

即较短的向量应立即开始自动重复。我敢肯定，这曾经对我有用（它在一个我已经运行了一百次的脚本中没有出现问题）。现在，我什至无法使上面的虚拟示例按我的意愿工作。我缺少什么？

I.e. the shorter vector should just start repeating itself automatically. I'm pretty certain this used to work for me (it's in a script that I've been running a hundred times before without problems). Now I can't even get the above dummy example to work like I want to. What am I missing?

推荐答案

如果可以将向量均匀回收到data.frame中，则不会得到错误或警告：

If the vector can be evenly recycled, into the data.frame, you do not get and error or a warning:

df <- data.frame(x = 1:10)
df$z <- 1:5

这可能就是您以前遇到的。

This may be what you were experiencing before.

您可以使用 rep_len 使向量适应您的要求：

You can get your vector to fit as you mention with rep_len:

df$y <- rep_len(1:3, length.out=10)

这将导致

df
    x z y
1   1 1 1
2   2 2 2
3   3 3 3
4   4 4 1
5   5 5 2
6   6 1 3
7   7 2 1
8   8 3 2
9   9 4 3
10 10 5 1

请注意的 rep_len 中，可以使用更常见的 rep 函数：

Note that in place of rep_len, you could use the more common rep function:

df$y <- rep(1:3,len=10)

从帮助文件中获取 rep ：

rep.int 和 rep_len 是两种常见情况下的简化版本。它们不是通用的。

rep.int and rep_len are faster simplified versions for two common cases. They are not generic.

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