Printing of data.table only works on the second call. Strange behavior

Asked Aug 01 '18 at 08:47

Active Aug 01 '18 at 08:47

Viewed 19 times

I'm running the latest data.table version:

> packageVersion("data.table")
#[1] ‘1.11.4’

Let's consider this example:

df <- data.frame(id = c(rep(1,5),rep(2,4)) ,subgrp = rep(letters[1:3],each=3),value = 1:9,stringsAsFactors = FALSE)
result<-
setDT(df)[,.(first_subgrp = subgrp[1],
             sum_val      = sum(value)),by="id"][,gt_15 := ifelse(sum_val > 15, T, F)]
result #nothing happens
result

slightly different version but same behavior.

df <- data.frame(id = c(rep(1,5),rep(2,4)) ,subgrp = rep(letters[1:3],each=3),value = 1:9,stringsAsFactors = FALSE)
result<-
    as.data.table(df)[,.(first_subgrp = subgrp[1],
                         sum_val      = sum(value)),by="id"][,gt_15 := ifelse(sum_val > 15, T, F)]
result #nothing happens again.
result

Question: Why is the data.table df only printed on the second "call".

asked Aug 01 '18 at 08:47

Andre Elrico

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This is, in fact, very much expected behavior: https://cran.r-project.org/web/packages/data.table/vignettes/datatable-faq.html#why-do-i-have-to-type-dt-sometimes-twice-after-using-to-print-the-result-to-console – MichaelChirico Aug 01 '18 at 08:50
Haa! Nicely said! Thanks. Let me read this! – Andre Elrico Aug 01 '18 at 08:53
A big gotcha of `data.table`, but after using `:=` sometimes you should wrap in `[]` to force printing. – MichaelChirico Aug 01 '18 at 08:54

Printing of data.table only works on the second call. Strange behavior

0 Answers0