add format_list_item.data.frame (#6593)

* Closes #6592, nested frames break if any are just 1-column

* typo

* upd tests

* fix typo in test

* style, tweaks

* refine NEWS

* fix link in NEWS

* Add as contributor

---------

Co-authored-by: Bill Evans <[email protected]>
Co-authored-by: Michael Chirico <[email protected]>
Co-authored-by: Michael Chirico <[email protected]>

Author: r2evans

DESCRIPTION

@@ -99,5 +99,6 @@ Authors@R: c(
   person("Elise", "Maigné",        role="ctb"),
   person("Vincent", "Rocher",      role="ctb"),
   person("Vijay", "Lulla",         role="ctb"),
-  person("Aljaž", "Sluga",         role="ctb")
+  person("Aljaž", "Sluga",         role="ctb"),
+  person("Bill", "Evans",          role="ctb")
   )

NAMESPACE

@@ -201,6 +201,7 @@ S3method(format_col, POSIXct)
 S3method(format_col, expression)
 export(format_list_item)
 S3method(format_list_item, default)
+S3method(format_list_item, data.frame)
 
 export(fdroplevels, setdroplevels)
 S3method(droplevels, data.table)

NEWS.md

@@ -113,6 +113,8 @@ rowwiseDT(
 
 13. `rbindlist(l, use.names=TRUE)` can now handle different encodings for the column names in different entries of `l`, [#5452](https://github.com/Rdatatable/data.table/issues/5452). Thanks to @MEO265 for the report, and Benjamin Schwendinger for the fix.
 
+14. Added a `data.frame` method for `format_list_item()` to fix error printing data.tables with columns containing 1-column data.frames, [#6592](https://github.com/Rdatatable/data.table/issues/6592). Thanks to @r2evans for the bug report and fix.
+
 ## NOTES
 
 1. Tests run again when some Suggests packages are missing, [#6411](https://github.com/Rdatatable/data.table/issues/6411). Thanks @aadler for the note and @MichaelChirico for the fix.

R/print.data.table.R

@@ -247,6 +247,11 @@ format_list_item.default = function(x, ...) {
   }
 }
 
+# #6592 -- nested 1-column frames breaks printing
+format_list_item.data.frame = function(x, ...) {
+  paste0("<", class1(x), paste_dims(x), ">")
+}
+
 # FR #1091 for pretty printing of character
 # TODO: maybe instead of doing "this is...", we could do "this ... test"?
 # Current implementation may have issues when dealing with strings that have combinations of full-width and half-width characters,

inst/tests/tests.Rraw

@@ -20651,3 +20651,16 @@ test(2298.2, rbindlist(list(y,x), use.names=TRUE), data.table("\u00f6"=c(4,2), "
 set(y, j="\u00e4", value=NULL)
 test(2298.3, rbindlist(list(x,y), use.names=TRUE, fill=TRUE), data.table("\u00e4"=c(1,NA), "\u00f6"=c(2,4), "\u00fc"=c(3,5)))
 test(2298.4, rbindlist(list(y,x), use.names=TRUE, fill=TRUE), data.table("\u00f6"=c(4,2),  "\u00fc"=c(5,3), "\u00e4"=c(NA,1)))
+
+# #6592: printing nested single-column frames
+test(2299.01, format_list_item(data.frame(a=1)),                      output="<data.frame[1x1]>")
+test(2299.02, format_list_item(data.frame(a=1)[0,,drop=FALSE]),       output="<data.frame[0x1]>")
+test(2299.03, format_list_item(data.frame(a=1)[,0]),                  output="<data.frame[1x0]>")
+test(2299.04, format_list_item(data.frame(a=1, b=2)[0,,drop=FALSE]),  output="<data.frame[0x2]>")
+test(2299.06, format_list_item(data.table(a=1)),                      output="<data.table[1x1]>")
+test(2299.07, format_list_item(data.table(a=numeric())),              output="<data.table[0x1]>")
+test(2299.08, format_list_item(data.table()),                         output="<data.table[0x0]>")
+test(2299.09, format_list_item(data.table(a=numeric(), b=numeric())), output="<data.table[0x2]>")
+test(2299.10, data.table(a=1),                                        output="a\n1: *1")
+test(2299.11, data.table(a=list(data.frame(b=1))),                    output="a\n1: <data.frame[1x1]>")
+test(2299.12, data.table(a=list(data.table(b=1))),                    output="a\n1: <data.table[1x1]>")