在 for 循环中使用 split()

Question

我想创建一个循环，对每个变量的因子水平进行汇总拆分。例如，如果我想在“分组”变量中按因子级别进行汇总拆分，我会使用：

df %>%
select(grouping, length, weight) %>%
split(.$grouping) %>%
map(summary)

但是，我不确定如何将其放入一个循环中，以便根据我的数据框中每个感兴趣的变量的因子水平得到一个摘要。

例如，我可以使用以下方法获取数据框第 3 列和第 4 列中变量的summary()：

# Dummy data
length = sample(30:60, 10, replace = FALSE)  
weight = sample(50:70, 10, replace = FALSE)
grouping = c("A", "A", "B", "A", "B", "A", "B", "B", "B", "A")
colour = c("Blue", "Green", "Green", "Green", "Blue", "Blue", "Blue", "Green", "Blue", "Green")
type = c("Case", "Control", "Case", "Case", "Case", "Control", "Control", "Case", "Control", "Case")
df = data.frame(length, weight, grouping, colour, type)

# Variables to loop
colNames <- names(df)[c(3:4)]

# Summary
for(i in colNames){
  # Summary
  summary <- df %>%
    select(length, weight, .$colNames[i]) %>%
    summary()
  
  print(summary)
}

但是当按每个变量的因子水平分割时我不能这样做：

# Variables to loop 
colNames = names(df)[c(3,4)]

# Summary 
for(i in colNames){
df %>%
select(length, weight, .$colNames[i]) %>%
split(.$colNames[i]) %>%
summary()
}

我认为split(.colNames) 是问题所在，但我不确定如何解决。感谢您的帮助！

Answer 1

您的代码有两个问题：

1. i 已经是您的列的名称。因此.$colNames[i] 是NULL。这个问题已经出现在select。
2. 如果您想使用包含列名的变量访问数据框中的列，那么$ 将不起作用。请改用[[。

# Dummy data
set.seed(42)
length <- sample(30:60, 10, replace = FALSE)
weight <- sample(50:70, 10, replace = FALSE)
grouping <- c("A", "A", "B", "A", "B", "A", "B", "B", "B", "A")
colour <- c("Blue", "Green", "Green", "Green", "Blue", "Blue", "Blue", "Green", "Blue", "Green")
type <- c("Case", "Control", "Case", "Case", "Case", "Control", "Control", "Case", "Control", "Case")
df <- data.frame(length, weight, grouping, colour, type)

# Variables to loop
colNames <- names(df)[c(3:4)]

library(dplyr)
library(purrr)

# Summary
for (i in colNames) {
  df %>%
    select(length, weight, all_of(i)) %>%
    split(.[[i]]) %>% 
    map(summary) %>% 
    map(print)
}

#>      length         weight       grouping        
#>  Min.   :33.0   Min.   :52.0   Length:5          
#>  1st Qu.:34.0   1st Qu.:53.0   Class :character  
#>  Median :36.0   Median :54.0   Mode  :character  
#>  Mean   :40.6   Mean   :59.2                     
#>  3rd Qu.:46.0   3rd Qu.:67.0                     
#>  Max.   :54.0   Max.   :70.0                     
#>      length       weight       grouping        
#>  Min.   :30   Min.   :58.0   Length:5          
#>  1st Qu.:39   1st Qu.:60.0   Class :character  
#>  Median :44   Median :63.0   Mode  :character  
#>  Mean   :44   Mean   :62.2                     
#>  3rd Qu.:47   3rd Qu.:64.0                     
#>  Max.   :60   Max.   :66.0                     
#> NULL
#>      length         weight        colour         
#>  Min.   :33.0   Min.   :52.0   Length:5          
#>  1st Qu.:39.0   1st Qu.:53.0   Class :character  
#>  Median :44.0   Median :58.0   Mode  :character  
#>  Mean   :41.8   Mean   :57.4                     
#>  3rd Qu.:46.0   3rd Qu.:60.0                     
#>  Max.   :47.0   Max.   :64.0                     
#>      length         weight      colour         
#>  Min.   :30.0   Min.   :54   Length:5          
#>  1st Qu.:34.0   1st Qu.:63   Class :character  
#>  Median :36.0   Median :66   Mode  :character  
#>  Mean   :42.8   Mean   :64                     
#>  3rd Qu.:54.0   3rd Qu.:67                     
#>  Max.   :60.0   Max.   :70