r - 在每次迭代 lapply 时打印，以便输出在列表元素之间

Question

似乎是一个初级的问题。有没有办法到print()或 message()在函数的迭代之间，以便打印在控制台输出中的列表元素之间。例子:

two_sq <- function (x) {
  print(paste("this is ", x))
  x^2
}
lapply(1:3, two_sq)

给出:

    # [1] "this is  1"
    # [1] "this is  2"
    # [1] "this is  3"
    # [[1]]
    # [1] 1

    # [[2]]
    # [1] 4

    # [[3]]
    # [1] 9

所需输出:

# [1] "this is  1"

# # [[1]]
# # [1] 1

# [2] "this is  2"

# # [[2]]
# # [1] 4

# [3] "this is  3"

# # [[3]]
# # [1] 9

Answer 1

two_sq <- function (x) {
    print(paste("this is ", x))
    print(x^2)
}
invisible(lapply(1:3, two_sq))

# [1] "this is  1"
# [1] 1
# [1] "this is  2"
# [1] 4
# [1] "this is  3"
# [1] 9