apply() 在检查 data.frame 中的列类时不起作用 [英] apply() not working when checking column class in a data.frame
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问题描述
我有一个数据框.我想检查每一列的 class
.
I have a dataframe. I want to inspect the class
of each column.
x1 = rep(1:4, times=5)
x2 = factor(rep(letters[1:4], times=5))
xdat = data.frame(x1, x2)
> class(xdat)
[1] "data.frame"
> class(xdat$x1)
[1] "integer"
> class(xdat$x2)
[1] "factor"
然而,想象一下我有很多列,因此需要使用 apply()
来帮助我完成这个技巧.但它不起作用.
However, imagine that I have many columns and therefore need to use apply()
to help me do the trick. But it's not working.
apply(xdat, 2, class)
x1 x2
"character" "character"
为什么我不能使用apply()
查看每一列的数据类型?或者我应该怎么做?
Why cannot I use apply()
to see the data type of each column? or What I should do?
谢谢!
推荐答案
你可以使用
sapply(xdat, class)
# x1 x2
# "integer" "factor"
使用 apply
会将输出强制转换为 matrix
并且矩阵只能包含一个类".如果有字符"列,则结果将是单个字符"类.了解这个检查
using apply
would coerce the output to matrix
and matrix can hold only a single 'class'. If there are 'character' columns, the result would be a single 'character' class. To understand this check
str(apply(xdat, 2, I))
#chr [1:20, 1:2] "1" "2" "3" "4" "1" "2" "3" "4" "1" ...
#- attr(*, "dimnames")=List of 2
# ..$ : NULL
# ..$ : chr [1:2] "x1" "x2"
现在,如果我们检查
str(lapply(xdat, I))
#List of 2
#$ x1:Class 'AsIs' int [1:20] 1 2 3 4 1 2 3 4 1 2 ...
#$ x2: Factor w/ 4 levels "a","b","c","d": 1 2 3 4 1 2 3 4 1 2 ...
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