CODEWITHSUNDEEP
r
John Chrysostom
John Chrysostom

Reputation: 3983

rbind and mapply - getting a matrix rather than a data frame

So, I'm trying to pass lists to a function that returns a data frame via mapply, then use do.call to rbind them all together into a single data frame.

Here's some dummy code:

var_1 <- list(1, 2)
var_2 <- list(3, 4)

output <- do.call(
    rbind,
    mapply(
      function(x, y) {return(data.frame(x, y, x+y))},
      var_1,
      var_2
    )
  )

Expected result: a data frame with 2 rows and 3 columns.

Actual result: a 6x1 matrix.

Any ideas on what I'm doing wrong here?

Upvotes: 1

Views: 1153

Answers (1)

MrFlick
MrFlick

Reputation: 206401

When using do.call you need to pass in a list of parameters. Currently your mapply call doesn't reuturn a list, it simplifies the result into a matrix. What you want is to prevent the simplification. You can either set the SIMPLIFY= parameter

output <- do.call(
    rbind,
    mapply(
      function(x, y) {return(data.frame(x, y, x+y))},
      var_1,
      var_2, SIMPLIFY=FALSE
    )
  )

or just use Map() which always returns a list

output <- do.call(
    rbind,
    Map(
      function(x, y) {return(data.frame(x, y, x+y))},
      var_1,
      var_2
    )
  )

Upvotes: 5

Related Questions