Question

我有一个列表，其中包含每个列表变量中的多个列。以下数据，

> str(A)
List of 4
 $ 1:Classes ‘nfnGroupedData’, ‘nfGroupedData’, ‘groupedData’ and 'data.frame': 220 obs. of  4 variables:
  ..$ weight: num [1:220] 42 51 59 64 76 93 106 125 149 171 ...
  ..$ Time  : num [1:220] 0 2 4 6 8 10 12 14 16 18 ...
  ..$ Chick : Ord.factor w/ 50 levels "18"<"16"<"15"<..: 15 15 15 15 15 15 15 15 15 15 ...
  ..$ Diet  : Factor w/ 4 levels "1","2","3","4": 1 1 1 1 1 1 1 1 1 1 ...
  ..- attr(*, "formula")=Class 'formula' length 3 weight ~ Time | Chick
  .. .. ..- attr(*, ".Environment")=<environment: R_EmptyEnv> 
  ..- attr(*, "outer")=Class 'formula' length 2 ~Diet
  .. .. ..- attr(*, ".Environment")=<environment: R_EmptyEnv> 
  ..- attr(*, "labels")=List of 2
  .. ..$ x: chr "Time"
  .. ..$ y: chr "Body weight"
  ..- attr(*, "units")=List of 2
  .. ..$ x: chr "(days)"
  .. ..$ y: chr "(gm)"
 $ 2:Classes ‘nfnGroupedData’, ‘nfGroupedData’, ‘groupedData’ and 'data.frame': 120 obs. of  4 variables:
  ..$ weight: num [1:120] 40 50 62 86 125 163 217 240 275 307 ...
  ..$ Time  : num [1:120] 0 2 4 6 8 10 12 14 16 18 ...
  ..$ Chick : Ord.factor w/ 50 levels "18"<"16"<"15"<..: 30 30 30 30 30 30 30 30 30 30 ...
  ..$ Diet  : Factor w/ 4 levels "1","2","3","4": 2 2 2 2 2 2 2 2 2 2 ...
  ..- attr(*, "formula")=Class 'formula' length 3 weight ~ Time | Chick
  .. .. ..- attr(*, ".Environment")=<environment: R_EmptyEnv> 
  ..- attr(*, "outer")=Class 'formula' length 2 ~Diet
  .. .. ..- attr(*, ".Environment")=<environment: R_EmptyEnv> 
  ..- attr(*, "labels")=List of 2
  .. ..$ x: chr "Time"
  .. ..$ y: chr "Body weight"
  ..- attr(*, "units")=List of 2
  .. ..$ x: chr "(days)"
  .. ..$ y: chr "(gm)"
 $ 3:Classes ‘nfnGroupedData’, ‘nfGroupedData’, ‘groupedData’ and 'data.frame': 120 obs. of  4 variables:
  ..$ weight: num [1:120] 42 53 62 73 85 102 123 138 170 204 ...
  ..$ Time  : num [1:120] 0 2 4 6 8 10 12 14 16 18 ...
  ..$ Chick : Ord.factor w/ 50 levels "18"<"16"<"15"<..: 34 34 34 34 34 34 34 34 34 34 ...
  ..$ Diet  : Factor w/ 4 levels "1","2","3","4": 3 3 3 3 3 3 3 3 3 3 ...
  ..- attr(*, "formula")=Class 'formula' length 3 weight ~ Time | Chick
  .. .. ..- attr(*, ".Environment")=<environment: R_EmptyEnv> 
  ..- attr(*, "outer")=Class 'formula' length 2 ~Diet
  .. .. ..- attr(*, ".Environment")=<environment: R_EmptyEnv> 
  ..- attr(*, "labels")=List of 2
  .. ..$ x: chr "Time"
  .. ..$ y: chr "Body weight"
  ..- attr(*, "units")=List of 2
  .. ..$ x: chr "(days)"
  .. ..$ y: chr "(gm)"
 $ 4:Classes ‘nfnGroupedData’, ‘nfGroupedData’, ‘groupedData’ and 'data.frame': 118 obs. of  4 variables:
  ..$ weight: num [1:118] 42 51 66 85 103 124 155 153 175 184 ...
  ..$ Time  : num [1:118] 0 2 4 6 8 10 12 14 16 18 ...
  ..$ Chick : Ord.factor w/ 50 levels "18"<"16"<"15"<..: 44 44 44 44 44 44 44 44 44 44 ...
  ..$ Diet  : Factor w/ 4 levels "1","2","3","4": 4 4 4 4 4 4 4 4 4 4 ...
  ..- attr(*, "formula")=Class 'formula' length 3 weight ~ Time | Chick
  .. .. ..- attr(*, ".Environment")=<environment: R_EmptyEnv> 
  ..- attr(*, "outer")=Class 'formula' length 2 ~Diet
  .. .. ..- attr(*, ".Environment")=<environment: R_EmptyEnv> 
  ..- attr(*, "labels")=List of 2
  .. ..$ x: chr "Time"
  .. ..$ y: chr "Body weight"
  ..- attr(*, "units")=List of 2
  .. ..$ x: chr "(days)"
  .. ..$ y: chr "(gm)"

我想取每个列表组件中$ weight列的平均值并将其作为向量返回。我试图使用sapply但没有结果。什么是正确的语法？

Answer 1

您可以直接使用sapply

  sapply(A, function(x) mean(x$weight, na.rm=TRUE))

使用可重现的例子

  library(nlme)
  A <- list(Orthodont, Orthodont)
  sapply(A, function(x) mean(x$age))
  #[1] 11 11

用sapply循环遍历列表对象

1 个答案: