删除R中的常量列 [英] Removal of constant columns in R

问题描述

当我收到此错误时我正在使用prcomp函数

I was using the prcomp function when I received this error

Error in prcomp.default(x, ...) : 
cannot rescale a constant/zero column to unit variance

我知道我可以扫描我的手动输入数据，但是R中是否有任何函数或命令可以帮助我删除这些常量变量？
我知道这是一个非常简单的任务，但我从未遇到过执行此操作的任何函数。

I know I can scan my data manually but is there any function or command in R that can help me remove these constant variables? I know this is a very simple task, but I have never been across any function that does this.

谢谢，

推荐答案

此处的问题是您的列方差等于零。您可以通过这种方式检查数据帧的哪一列是常量，例如：

The problem here is that your column variance is equal to zero. You can check which column of a data frame is constant this way, for example :

df <- data.frame(x=1:5, y=rep(1,5))
df
#   x y
# 1 1 1
# 2 2 1
# 3 3 1
# 4 4 1
# 5 5 1

# Supply names of columns that have 0 variance
names(df[, sapply(df, function(v) var(v, na.rm=TRUE)==0)])
# [1] "y" 

因此，如果要排除这些列，可以使用：

So if you want to exclude these columns, you can use :

df[,sapply(df, function(v) var(v, na.rm=TRUE)!=0)]

编辑：实际上，使用 apply 更为简单。像这样的东西：

EDIT : In fact it is simpler to use apply instead. Something like this :

df[,apply(df, 2, var, na.rm=TRUE) != 0]

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