Data.frame成为过滤/子集后的因子/向量 [英] Data.frame becomes factor/vector after filtering/subsetting
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问题描述
我有一个数据框架,一列如下:
I have a data.frame with one column, like so:
>d = data.frame(animal=c("horse","dog","cat"))
然后我将其排除所有项目也存在于向量中。例如:
then I filter it by excluding all items also present in a vector. e.g.:
> res = d[!(d$animal %in% c("horse")),]
> res
[1] dog cat
Levels: cat dog horse
>class(res)
[1] "factor"
这里发生了什么?
推荐答案
欢迎你刚刚被 drop
烦恼所困:你需要明确告诉R不要放到一维:
Welcome to R. You've just been bitten by the drop
annoyance: you need to explicitly tell R not to "drop to one-dimension":
res = d[!(d$animal %in% c("horse")), , drop = FALSE]
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