r - 在 for 循环中使用 split()

Question

我想创建一个循环来获取每个变量的因子水平的汇总拆分。例如，如果我想在“分组”变量中按因子级别进行汇总拆分，我将使用:

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

但是，我不确定如何将其放入循环中，以便根据数据框中每个感兴趣的变量的因子水平获得摘要。
例如，我可以得到 summary()对于数据框第 3 列和第 4 列中的变量，使用:

# 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()
}

我图 split(.colNames)是问题所在，但我不知道如何解决。感谢您的任何帮助!

Answer 1

您的代码有两个问题:

i已经是您的列的名称。因此 .$colNames[i]是 NULL .此问题已在 select 中出现.

如果要使用包含列名的变量访问数据框中的列，则 $不管用。而是使用 [[ .

# 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