I am trying to play with function of lapply
lapply(1:3, function(i) print(i))
# [1] 1
# [1] 2
# [1] 3
# [[1]]
# [1] 1
# [[2]]
# [1] 2
# [[3]]
# [1] 3
I understand that lapply should be able to perform print (i) against each element i among 1:3
But why the output looks like this.
Besides, when I use unlist, I get the output like the following
unlist(lapply(1:3, function(i) print(i)))
# [1] 1
# [1] 2
# [1] 3
# [1] 1 2 3
The description of lapply function is the following:
"lapply returns a list of the same length as X, each element of which is the result of applying FUN to the corresponding element of X."
Your example:
lapply(1:3, function(x) print(x))
Prints the object x and returns a list of length 3.
str(lapply(1:3, function(x) print(x)))
# [1] 1
# [1] 2
# [1] 3
# List of 3
# $ : int 1
# $ : int 2
# $ : int 3
There are a few ways to avoid this as mentioned in the comments:
1) Using invisible
lapply(1:3, function(x) invisible(x))
# [[1]]
# [1] 1
# [[2]]
# [1] 2
# [[3]]
# [1] 3
unlist(lapply(1:3, function(x) invisible(x)))
# [1] 1 2 3
2) Without explicitly printing inside the function
unlist(lapply(1:3, function(x) x))
# [1] 1 2 3
3) Assining the list to an object:
l1 <- lapply(1:3, function(x) print(x))
unlist(l1)
# [1] 1 2 3
l <- lapply(1:5, function(x) print(i))