bug fix: truncate wide columns in print.data.table by venom1204 · Pull Request #7788 · Rdatatable/data.table

venom1204 · 2026-06-10T21:12:31Z

closes #7718
sorry for the new pr ,as there was some error in the previous one

here is the summary of teh previous pr

the earlier pr mainly used a fixed getOption("width") - 5L style truncation approach which worked for some simple cases but failed once row labels became larger (for example 1000000:) because the full rendered line width was not being accounted for correctly.

in this updated implementation, the truncation width is now calculated dynamically using the actual row label width and console width instead of a fixed constant.
i also added a saftey handelling using allowNA=TRUE in nchar() calls to avoid invalid width failures during tests,while preserving thr original datatable.prettyprint.char.

with these changes the ouput now takes the full options(width) limit for the entire rendered line.
hi @joshhwuu @tdhock can you please have a look at it when you got time ,
thanks

codecov · 2026-06-10T21:19:52Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.85%. Comparing base (d65e46f) to head (aa8c344).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7788   +/-   ##
=======================================
  Coverage   98.85%   98.85%           
=======================================
  Files          87       87           
  Lines       17128    17137    +9     
=======================================
+ Hits        16932    16941    +9     
  Misses        196      196

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github-actions · 2026-06-10T21:36:39Z

No obvious timing issues in HEAD=issue771188

Generated via commit aa8c344

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	2 minutes and 27 seconds
Installing different package versions	22 seconds
Running and plotting the test cases	5 minutes and 12 seconds

joshhwuu · 2026-06-10T22:25:01Z

 }

 format_col.default = function(x, ...) {
+  dots = list(...)


could you explain the motivation behind this dots = list(...) pattern? imo it makes the code a lot harder to read, would rather us be more specific about method contracts and declare it as a parameter

it was done to avoid the codoc mismatch between teh doc and the code , now i have updated the doc and reverted it

joshhwuu · 2026-06-10T22:26:55Z


 11. `between()` now supports `Date` and `IDate` bounds with default `NAbounds=TRUE`, avoiding errors like "Not yet implemented NAbounds=TRUE for this non-numeric and non-character type" when date bounds contain `NA`, [#7281](https://github.com/Rdatatable/data.table/issues/7281). Thanks @grcatlin for the report and fix, and @ben-schwen and @aitap for assistance.

+12. `print.data.table()` now correctly truncates long character columns and list-column summaries to avoid horizontal console overflow, [#7718](https://github.com/Rdatatable/data.table/issues/7718). When `datatable.prettyprint.char` is `NULL` (the default), the truncation limit is now dynamically calculated as `getOption("width") - 5L`. Thanks @tdhock for the report and @venom1204 for the fix.


is this still true? also we may not want to be too verbose about implementation details here

sorry for the news entry I simply gave the previous file forgot to modify it.

tdhock

this looks good, but can you please add some examples in Rd and PR comments (with output) ?

venom1204 · 2026-06-11T18:13:42Z

this looks good, but can you please add some examples in Rd and PR comments (with output) ?

> library(data.table)
data.table 1.18.99 IN DEVELOPMENT built 2026-06-10 20:33:59 UTC; root using 6 threads (see ?getDTthreads).  Latest news: r-datatable.com
> 
> options(width = 20, datatable.prettyprint.char = NULL)
data.table(x = "12345678901234567890")
                   x
              <char>
1: 12345678901234...
> options(width = 25, datatable.prettyprint.char = NULL)
DT = data.table(x = rep("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 1000000))
print(DT, topn = 1)
                        x
                   <char>
      1: ABCDEFGHIJKLM...
     ---                 
1000000: ABCDEFGHIJKLM...

hi @tdhock are these examples good or should i do it for some more examples.
thanks

joshhwuu · 2026-06-11T18:16:31Z


 11. `between()` now supports `Date` and `IDate` bounds with default `NAbounds=TRUE`, avoiding errors like "Not yet implemented NAbounds=TRUE for this non-numeric and non-character type" when date bounds contain `NA`, [#7281](https://github.com/Rdatatable/data.table/issues/7281). Thanks @grcatlin for the report and fix, and @ben-schwen and @aitap for assistance.

+12. `print.data.table()` now correctly truncates long character columns and list-column summaries to avoid horizontal console overflow, [#7718](https://github.com/Rdatatable/data.table/issues/7718). When `datatable.prettyprint.char` is `NULL` (the default), the truncation limit is now dynamically calculated based on the available console width. Thanks @tdhock for the report and @venom1204 for the fix.


instead of saying "now correctly", maybe we can say "now by default"? WDYT

yah i think that sounds good and more descriptive.

tdhock · 2026-06-12T14:24:34Z

+  data.table(x = "abcdefghijklmnopqrstuvwxyz", L = list(1:25))
+
+  # Dynamic truncation: Content shrinks as row labels grow
+  print(data.table(x = rep("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 1e6)), topn = 1)
+  options(old)


can you please show us the output of these commands in a PR comment?

> library(data.table) data.table 1.18.99 IN DEVELOPMENT built 2026-06-12 15:39:21 UTC; root using 6 threads (see ?getDTthreads). Latest news: r-datatable.com > options(width = 25, datatable.prettyprint.char = NULL) > data.table(x = "abcdefghijklmnopqrstuvwxyz", L = list(1:25)) x <char> 1: abcdefghijklmnopqrs... L <list> 1: 1,2,3,4,5,6,...[25] > print(data.table(x = rep("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 1e6)), topn = 1) x <char> 1: ABCDEFGHIJKLM... --- 1000000: ABCDEFGHIJKLM...

here is what i got as a result

new pr

b1412c1

venom1204 requested a review from MichaelChirico as a code owner June 10, 2026 21:12

venom1204 changed the title ~~new pr~~ bug fix: truncate wide columns in print.data.table Jun 10, 2026

venom1204 added 2 commits June 10, 2026 21:26

..

460da17

lint

74f6b1a

.

4fb6707

joshhwuu reviewed Jun 10, 2026

View reviewed changes

Comment thread inst/tests/tests.Rraw

joshhwuu reviewed Jun 10, 2026

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Comment thread R/print.data.table.R Outdated

joshhwuu reviewed Jun 10, 2026

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Comment thread R/print.data.table.R Outdated

joshhwuu reviewed Jun 10, 2026

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venom1204 added 2 commits June 10, 2026 22:59

updated list(...) , news, tests

72b6b72

lintr

6a1d3a8

tdhock requested changes Jun 11, 2026

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joshhwuu reviewed Jun 11, 2026

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venom1204 added 2 commits June 11, 2026 18:19

added examples in doc

741974b

added descriptive news

aa8c344

venom1204 requested review from joshhwuu and tdhock June 11, 2026 18:51

tdhock reviewed Jun 12, 2026

View reviewed changes


		11. `between()` now supports `Date` and `IDate` bounds with default `NAbounds=TRUE`, avoiding errors like "Not yet implemented NAbounds=TRUE for this non-numeric and non-character type" when date bounds contain `NA`, [#7281](https://github.com/Rdatatable/data.table/issues/7281). Thanks @grcatlin for the report and fix, and @ben-schwen and @aitap for assistance.

		12. `print.data.table()` now correctly truncates long character columns and list-column summaries to avoid horizontal console overflow, [#7718](https://github.com/Rdatatable/data.table/issues/7718). When `datatable.prettyprint.char` is `NULL` (the default), the truncation limit is now dynamically calculated as `getOption("width") - 5L`. Thanks @tdhock for the report and @venom1204 for the fix.

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venom1204 commented Jun 10, 2026 •

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