Converting a data.frame to a list of lists

Question

How can I convert a data.frame

df <- data.frame(id=c(\"af1\", \"af2\"), start=c(100, 115), end=c(114,121))

To a list of lists

Answer 1

In base R, it's quite a bit faster to use mapply instead of split or lapply - however, you have to invoke it via do.call so that each column is used independently.

df <- sleep

f <- function(df) {
  lapply(seq_len(nrow(df)), function(row) {
    df[row, , drop = FALSE]
  })
}

f2 <- function(df) {
  do.call("mapply", c(list, df, SIMPLIFY = FALSE, USE.NAMES=FALSE))
}

f3 <- function(df) {
  split(df, seq(nrow(df)))
}

microbenchmark::microbenchmark(f(df), f2(df), f3(df))
#> Unit: microseconds
#>    expr     min       lq     mean   median       uq       max neval
#>   f(df) 573.799 607.8375 759.1721 626.0095 752.9465  2861.961   100
#>  f2(df) 114.819 123.5190 155.5185 129.9210 141.4340  1375.573   100
#>  f3(df) 598.774 625.6025 813.6837 634.5855 684.3825 11230.678   100

^{Created on 2019-10-09 by the reprex package (v0.3.0)}