Add multiple output variables using purrr and a predefined function

Question

Take this simple dataset and function (representative of more complex problems):

x <- data.frame(a = 1:3, b = 2:4)
mult <- function(a,b,n) (a + b) * n
         


        

Answer 1

To mimic the input format for Map, we could call pmap from purrr in this way:

x[paste0("new",seq_along(ns))] <- pmap(list(x['a'], x['b'], ns), mult)

To fit this in a pipe:

x %>%
    {list(.['a'], .['b'], ns)} %>%
    pmap(mult) %>%
    setNames(paste0('new', seq_along(ns))) %>%
    cbind(x)

#   new1 new2 a b
# 1    3    6 1 2
# 2    5   10 2 3
# 3    7   14 3 4

Apparently, this looks ugly compared to the concise base R code. But I could not think of a better way.