R语言：lengths计算列表list中元素的个数

2024-07-01 16:18| 来源: 网络整理| 查看: 265

这次介绍一个大家可能会用到的函数，但是又与我们常用的函数有所区别。

lengths

一看，还以为是length函数，我们要介绍的函数后面多了一个s，专门用于计算列表list的长度，下面用例子来呈现我们的函数。

首先，我们先来介绍length函数，再来介绍lengths，最后对两个差异的地方进行对比，查看区别。

length

Get or set the length of vectors (including lists) and factors, and of any other R object for which a method has been defined

帮助文档内容：x是向量，因子，列表

> length(diag(4)) # = 16 (4 x 4) [1] 16 > length(1:5) [1] 5 > length(options()) # 12 or more [1] 76 > length(y ~ x1 + x2 + x3) # 3 [1] 3 > length(expression(x, {y require(stats) > fm1 length(fm1$call) # 3, lm() and two arguments. [1] 3 > length(formula(fm1)) # 3, ~ lhs rhs [1] 3 lengths

Get the length of each element of a list or atomic vector (is.atomic) as an integer or numeric vector.

x为列表、向量

> require(stats) > l l $`5` [1] 41 36 12 18 NA 28 23 19 8 NA 7 16 11 14 18 14 34 6 30 [20] 11 1 11 4 32 NA NA NA 23 45 115 37 $`6` [1] NA NA NA NA NA NA 29 NA 71 39 NA NA 23 NA NA 21 37 20 12 13 NA NA NA NA NA [26] NA NA NA NA NA $`7` [1] 135 49 32 NA 64 40 77 97 97 85 NA 10 27 NA 7 48 35 61 79 [20] 63 16 NA NA 80 108 20 52 82 50 64 59 $`8` [1] 39 9 16 78 35 66 122 89 110 NA NA 44 28 65 NA 22 59 23 31 [20] 44 21 9 NA 45 168 73 NA 76 118 84 85 $`9` [1] 96 78 73 91 47 32 20 23 21 24 44 21 28 9 13 46 18 13 24 16 13 23 36 7 14 [26] 30 NA 14 18 20 > lengths(l,use.names = F) [1] 31 30 31 31 30 > lengths(expression(u, v, 1+ 0:9)) [1] 1 1 3 > f f [1] 1 1 1 2 2 2 2 2 2 3 > dates dates $`1` [1] "2016-12-09 21:09:50 CST" "2016-12-09 21:09:51 CST" [3] "2016-12-09 21:09:52 CST" $`2` [1] "2016-12-09 21:09:53 CST" "2016-12-09 21:09:54 CST" [3] "2016-12-09 21:09:55 CST" "2016-12-09 21:09:56 CST" [5] "2016-12-09 21:09:57 CST" "2016-12-09 21:09:58 CST" $`3` [1] "2016-12-09 21:09:59 CST" > lengths(dates,use.names=F) [1] 3 6 1 lengths 和 length > f f [1] 1 1 1 2 2 2 2 2 2 3 > dates dates $`1` [1] "2016-12-09 21:09:50 CST" "2016-12-09 21:09:51 CST" [3] "2016-12-09 21:09:52 CST" $`2` [1] "2016-12-09 21:09:53 CST" "2016-12-09 21:09:54 CST" [3] "2016-12-09 21:09:55 CST" "2016-12-09 21:09:56 CST" [5] "2016-12-09 21:09:57 CST" "2016-12-09 21:09:58 CST" $`3` [1] "2016-12-09 21:09:59 CST" > lengths(dates,use.names=F) [1] 3 6 1 > length(dates) [1] 3

length得到的是list的个数，lengths是得到每个list下的个数。这个是计算时很重要。顿时感觉这个函数很神奇。哈哈哈！

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