来自字符和数字的数据框的子集字符列

Question

我有一个由数字和非数字列组成的数据框.

我想提取(子集)非数字列,所以字符为1.虽然我能够使用字符串对数字列进行子集化sub_num = x[sapply(x, is.numeric)],但我无法使用is.character表单执行相反的操作.谁能帮我？

Answer 1

如果您尝试仅选择字符列，可以使用dplyr::select_if()和 来完成is.character()。以dplyr::starwars样本数据为例：

library(dplyr)
starwars %>% 
  select_if(is.character) %>% 
  head(2)
# A tibble: 2 x 7
  name           hair_color skin_color eye_color gender homeworld species
  <chr>          <chr>      <chr>      <chr>     <chr>  <chr>     <chr>  
1 Luke Skywalker blond      fair       blue      male   Tatooine  Human  
2 C-3PO          NA         gold       yellow    NA     Tatooine  Droid 

或者，如果您尝试否定某种列类型，请注意语法略有不同：

starwars %>%  
  select_if(~!is.numeric(.)) %>% 
  head(2)

# A tibble: 2 x 10
    name           hair_color skin_color eye_color gender homeworld species films     vehicles  starships
    <chr>          <chr>      <chr>      <chr>     <chr>  <chr>     <chr>   <list>    <list>    <list>   
  1 Luke Skywalker blond      fair       blue      male   Tatooine  Human   <chr [5]> <chr [2]> <chr [2]>
  2 C-3PO          NA         gold       yellow    NA     Tatooine  Droid   <chr [6]> <chr [0]> <chr [0]>

Answer 2

好的,我做了一个关于我的想法的简短尝试.

我可以确认以下代码段正在运行:

str(d)
 'data.frame':  5 obs. of  3 variables:
  $ a: int  1 2 3 4 5
  $ b: chr  "a" "a" "a" "a" ...
  $ c: Factor w/ 1 level "b": 1 1 1 1 1


# Get all character columns
d[, sapply(d, class) == 'character']

# Or, for factors, which might be likely:
d[, sapply(d, class) == 'factor']

# If you want to get both factors and characters use
d[, sapply(d, class) %in% c('character', 'factor')]

使用正确的类,您的sapply-approach也应该起作用,至少只要您,在sapply函数之前插入缺失项.

!is.numeric如果您有不属于该组的类numeric, factor, character(POSIXct例如我经常使用的那个),那么使用的方法不能很好地扩展