R data.table apply function to rows using columns as arguments which returns a vector (i.e. multiple values)

Question

Let say I have below data.table-

library(data.table)
x = structure(list(f1 = 1:3, f2 = 3:5), .Names = c("f1", "f2"), row.names = c(NA, -3L), class = c("data.table", "data.frame"))

Now I want to apply below function on every rows-

func.text <- function(arg1,arg2){ return(c(10, arg1 + exp(arg2)))}

With that, I see below result-

> x[, func.text(f1, f2), by = seq_len(nrow(x))]
   seq_len        V1
1:       1  10.00000
2:       1  21.08554
3:       2  10.00000
4:       2  56.59815
5:       3  10.00000
6:       3 151.41316

However, I wanted to get 2 extra columns in the final result because this function returning 2 values, same number of rows as with original data.table.

Is there any way to do this?

s_baldur · Accepted Answer · 2019-10-25 13:31:51Z

3

Minimal changes to your original idea:

make the function return a list and
assign the result with :=

func.text <- function(arg1,arg2){ return(list(10, arg1 + exp(arg2)))}
x[, c("var1", "var2") := func.text(f1, f2), by = seq_len(nrow(x))]
x

   f1 f2      var2 var1
1:  1  3  21.08554   10
2:  2  4  56.59815   10
3:  3  5 151.41316   10

edited Oct 25, 2019 at 13:31

answered Oct 25, 2019 at 13:14

s_baldur

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2 Comments

Bogaso Over a year ago

Thanks for this awesome reply. One further question though. Let say instead of passing argument as the name of columns of data.table, can we just pass entire row as vector assuming all columns of data.table are numeric. The column name of my original data.table is variable therefore keep changing. So I am trying to avoid to pass the column names

s_baldur Over a year ago

@Bogaso Yes, you can do that easily.

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