从数据框中删除稀有因子水平的优雅方法

问题描述

我想按因子对数据帧进行子集化.我只想保留高于某个频率的因子水平.

I want to subset a dataframe by factor. I only want to retain factor levels above a certain frequency.

df <- data.frame(factor = c(rep("a",5),rep("b",5),rep("c",2)), variable = rnorm(12))

此代码创建数据框:

   factor    variable
1       a -1.55902013
2       a  0.22355431
3       a -1.52195456
4       a -0.32842689
5       a  0.85650212
6       b  0.00962240
7       b -0.06621508
8       b -1.41347823
9       b  0.08969098
10      b  1.31565582
11      c -1.26141417
12      c -0.33364069

而且我想删除重复少于 5 次的因子水平.我开发了一个 for 循环并且它正在工作:

And I want to drop factor levels which repeated less than 5 times. I developed a for-loop and it is working:

for (i in 1:length(levels(df$factor))){
  if(table(df$factor)[i] < 5){
    df.new <- df[df$factor != names(table(df$factor))[i],]
  }
}

但是否存在更快更漂亮的解决方案?

But do quicker and prettier solutions exists?

推荐答案

怎么样

df.new <- df[!(as.numeric(df$factor) %in% which(table(df$factor)<5)),]

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