How to get the name of each element of a list using lapply()?

Question

Imagine that I have the following list

> test <- list(\"a\" = 1, \"b\" = 2)

Each element of the list has a name :

>          


        

Answer 1

Assuming you meant for both elements of test to contain a 3-columned matrix, you can use mapply() and provide separately the list and the list's names:

  test <- list("a" = matrix(1, ncol = 3), "b" = matrix(2, ncol = 3))

  make_df <- function(x, y) {
    output <- data.frame(x)
    names(output) <- c("items", "type", y)
    return(output)
  }

  mapply(make_df, x = test, y = names(test), SIMPLIFY = FALSE)

which produces:

## $a
##   items type a
## 1     1    1 1
##
## $b
##   items type b
## 1     2    2 2

Update

To achieve the expected output you describe in your updated question:

test.names <- lapply(names(test), function(x) c("index", "type", x))
Map(setNames, test, test.names)

produces:

## $a
##      [,1] [,2] [,3]
## [1,]    1    1    1
## attr(,"names")
## [1] "a"     "index" "type"  
## 
## $b
##      [,1] [,2] [,3]
## [1,]    2    2    2
## attr(,"names")
## [1] "b"     "index" "type"