R the same element to sublists - r

Question

I have a list m containing sublists. One sublist is like:
> m[[1]]
$input
$input$a
[1] 1
$input$b
[1] 2
$input$c
[1] 3
$output
$output$y
[1] "big dog"
The entire list is:
[[1]]
[[1]]$input
[[1]]$input$a
[1] 1
[[1]]$input$b
[1] 2
[[1]]$input$c
[1] 3
[[1]]$output
[[1]]$output$y
[1] "big dog"
[[2]]
[[2]]$input
[[2]]$input$a
[1] 12
[[2]]$input$b
[1] 89
[[2]]$input$c
[1] 67
[[2]]$output
[[2]]$output$y
[1] "fat cat"
[[3]]
[[3]]$input
[[3]]$input$a
[1] 7
[[3]]$input$b
[1] 4
[[3]]$input$c
[1] 97
[[3]]$output
[[3]]$output$y
[1] "fat cat"
And the code is:
m<-list(
list(
input=list(a=1,b=2,c=3),
output=list(y="big dog")
),
list(
input=list(a=12,b=89,c=67),
output=list(y="fat cat")
),
list(
input=list(a=7,b=4,c=97),
output=list(y="fat cat")
)
)
Now I want to add to each subsublist named 'input' the same variable named type and containing value "pet" to have:
m
[[1]]
[[1]]$input
[[1]]$input$a
[1] 1
[[1]]$input$b
[1] 2
[[1]]$input$c
[1] 3
[[1]]$input$type
[1] "pet"
[[1]]$output
[[1]]$output$y
[1] "big dog"
[[2]]
[[2]]$input
[[2]]$input$a
[1] 12
[[2]]$input$b
[1] 89
[[2]]$input$c
[1] 67
[[2]]$input$type
[1] "pet"
[[2]]$output
[[2]]$output$y
[1] "fat cat"
[[3]]
[[3]]$input
[[3]]$input$a
[1] 7
[[3]]$input$b
[1] 4
[[3]]$input$c
[1] 97
[[3]]$input$type
[1] "pet"
[[3]]$output
[[3]]$output$y
[1] "fat cat"
I tried:
Map(function(u) c(u$input, type="pet"))
But it does not work as it filter the list :(
Do yo have any idea?

Answer 1

This should do the trick:
m2 <- lapply(m, modifyList, list(input=list(type="pet")))
## Check that it worked
str(m2[3])
# List of 1
# $ :List of 2
# ..$ input :List of 4
# .. ..$ a : num 7
# .. ..$ b : num 4
# .. ..$ c : num 97
# .. ..$ type: chr "pet"
# ..$ output:List of 1
# .. ..$ y: chr "fat cat"
If the formulation above seems a bit opaque, try running the following, which will likely help you to see how modifyList() works in this case:
m[[1]]
list(input=list(type="pet"))
modifyList(m[[1]], list(input=list(type="pet")))

Answer 2

If I understand you correctly, I think you just want
m<-lapply(m, function(x) {x$input$type<-"pet";x})
That will add $type="pet" to every input in your list. Resulting in
list(
list(
input = list(a = 1, b = 2, c = 3, type = "pet"),
output = list(y = "big dog")
),
list(
input = list(a = 12, b = 89, c = 67, type = "pet"),
output = list(y = "fat cat")
),
list(
input = list(a = 7, b = 4, c = 97, type = "pet"),
output = list(y = "fat cat")
)
)