[R] Create a data.table by looping over variable names

András Tajti atajti at gmail.com
Wed Dec 16 13:12:14 CET 2015

Dear Matteo,
I found a one-liner solution to this problem:
n <- 100
data.table(i0 = 100)[, (paste0("i", 1:n)) := 100]

the data.table(i0=100) creates a one column-one row data.table,

Between the [] brakets i create a column name vector with paste, and
surround it with () to make it recognised as names (for details, look at
the Dateails of ?`:=`), and it will append columns to the i0 data.table.

This cannot be done with a 0-column data.table.

Good luck:
András Tajti

On 16 December 2015 at 12:53, Matteo Richiardi <matteo.richiardi at gmail.com>

> I apologise for this very basic question, but I found no answers on the
> web.
> I want to create a data.table with n columns, named i1 ... i'n', with only
> one row with value = 100 for every variable.
> I can do it "by hand":
> M.dt <- data.table(i1=100,i2=100,i3=100)
> but I would like to make it in a loop, as 'n' is large in my case.
> Thanks.
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