基于计数的数据帧中所有因子变量的折叠因子水平

问题描述

我只想根据频率保持前2个因素水平，并将所有其他因素归类为其他".我试过了，但没有帮助.

I would like to keep only the top 2 factor levels based on the frequency and group all other factors into Other. I tried this but it doesnt help.

df=data.frame(a=as.factor(c(rep('D',3),rep('B',5),rep('C',2))),
              b=as.factor(c(rep('A',5),rep('B',5))),
              c=as.factor(c(rep('A',3),rep('B',5),rep('C',2))))

myfun=function(x){
    if(is.factor(x)){
        levels(x)[!levels(x) %in% names(sort(table(x),decreasing = T)[1:2])]='Others'
    }
}

df=as.data.frame(lapply(df, myfun))

预期产量

       a b      c
       D A      A
       D A      A
       D A      A
       B A      B
       B A      B
       B B      B
       B B      B
       B B      B
  others B others
  others B others

推荐答案

这可能会有点混乱，但这是通过基数R的一种方法，

This might get a bit messy, but here is one approach via base R,

fun1 <- function(x){levels(x) <-
                    c(names(sort(table(x), decreasing = TRUE)[1:2]),
                    rep('others', length(levels(x))-2));
                    return(x)}

不过，首先需要对上述功能进行重新排序，并且当OP在注释中指出时，正确的功能应该是

However the above function will need to first be re-ordered and as OP states in comment, the correct one will be,

fun1 <- function(x){ x=factor(x,
                     levels = names(sort(table(x), decreasing = TRUE)));
                     levels(x) <- c(names(sort(table(x), decreasing = TRUE)[1:2]),
                     rep('others', length(levels(x))-2));
                     return(x) }

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