删除少于n个值的列？ [英] drop columns that take less than n values?

问题描述

假设我有一个如下数据帧：

Suppose i have a data frame like the following:

df <- data.frame(v1 = sample(1:10, 100, replace = T), v2 = sample(LETTERS, 100, replace = T),
                 V3 = sample(letters, 100, replace = T), v4 = sample(1:15, 100, replace = T))

我想创建一个新的数据框df2仅包括超过10个值。因此，在此示例中，它将是v2，v3和v4。我怎样才能做到这一点？实际上，我的数据框有成千上万的列。

I would like to create a new data frame df2 only includes the columns that take more than 10 values. So, in this example it would be v2, v3, and v4. How can I do that? In practice my data frame has thousands of columns.

我尝试过：

df2 <- df %>% select(which(length(unique(.))>10))

推荐答案

或者，您可以使用 dplyr select_if（） $ c>，您可以在其中传递谓词以选择列：

Alternatively, you can use select_if() from dplyr where you can pass a function as predicate to select columns:

library(dplyr)
df %>% select_if(function(col) n_distinct(col) > 10)

#    v2 V3 v4
#1    T  a 12
#2    R  k  7
#3    L  l  1
# ...

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