头和尾不使用负数作为data.table的参数？ [英] head and tail doesn't take negative number as argument for data.table?

问题描述

为 data.table 头和尾 c>？是设计吗？

Why head and tail work differently for data.table? Is it by design?

> head(data.frame(x=1:10), -2)
  x
1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
> head(data.table(x=1:10), -2)
Error in seq_len(min(n, nrow(x))) : 
  argument must be coercible to non-negative integer
> tail(data.table(x=1:10), -2)
    x
1: NA
2: NA
3: NA
4: 10
> tail(data.frame(x=1:10), -2)
    x
3   3
4   4
5   5
6   6
7   7
8   8
9   9
10 10

推荐答案

是，之前报告过，＃2375 。现在已在 v1.8.11 中修正。从新闻 ：

Yes, this was reported before, #2375. This is now fixed in v1.8.11. From NEWS:

head（） tail（）现在正确处理负'n'值，＃2375。感谢Garrett See报告。此外，当 length（n）！= 1 时会导致错误。已添加测试。

head() and tail() handle negative 'n' values correctly now, #2375. Thanks to Garrett See for reporting. Also it results in an error when length(n) != 1. Tests added.

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