How to collapse all character vectors in a list

Question

I have a dataframe with one specific column that is made up of a list of characters as follows:

a <- list("dyspla", c("dyspla", "dyspla"), "carcin",
          c("tumour", "dyspla"), character(0), character(0),
          c("carcin", "dyspla"), character(0), character(0), "dyspla")

I want it to be a character vector with the character vectors in the list collapsed as follows

c("dyspla","dyspla,dyspla","carcin","tumour,dyspla","carcin,dyspla","dyspla")

paste(a,collapse=" ") collapses everything together. How to collapse by vector within the list?

Answer 1

A possible solution:

sapply(a[!!lengths(a)], toString)

Or with purrr's is_empty function:

sapply(a[!sapply(a, purrr::is_empty)], toString)

which both give:

[1] "dyspla"         "dyspla, dyspla" "carcin"         "tumour, dyspla" "carcin, dyspla" "dyspla"

Alternatively with paste:

sapply(a[!sapply(a, purrr::is_empty)], paste, collapse = ',')

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In response to your comment:

If you want to keep the empty character, you can just do sapply(a, toString) or sapply(a, paste, collapse = ',').