r 在lapply函数中保留名称

Posted 2021-05-23

  # Dummy example to generate 2 lists. One without and other with names.
  # cf : https://stackoverflow.com/questions/9469504/access-and-preserve-list-names-in-lapply-function/18520422#18520422
  
  # Get numeric columns from iris
  cols <- names(which(sapply(iris, is.numeric)))
  
  # Compute mean from each numeric column
  res <- lapply(cols, function(i) {
    mean(iris[,i])
  })
  # [[1]]
  # [1] 5.843333
  # 
  # [[2]]
  # [1] 3.057333
  # 
  # [[3]]
  # [1] 3.758
  # 
  # [[4]]
  # [1] 1.199333
  
  res <- lapply(setNames(cols,cols), function(i) {
    mean(iris[,i])
  })
  
  # $Sepal.Length
  # [1] 5.843333
  # 
  # $Sepal.Width
  # [1] 3.057333
  # 
  # $Petal.Length
  # [1] 3.758
  # 
  # $Petal.Width
  # [1] 1.199333