Your message dated Fri, 25 Apr 2014 09:03:19 +0200 with message-id <[email protected]> and subject line Re: Bug#725426: gawk(1) man page is unclear regarding for loops with multi-index arrays has caused the Debian Bug report #725426, regarding gawk(1) man page is unclear regarding for loops with multi-index arrays to be marked as done.
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--- Begin Message ---Package: gawk Version: 1:4.0.1+dfsg-2.1 Severity: normal Hello, thanks for maintaining gawk in Debian! I noticed that the gawk(1) man page is somewhat misleading regarding for loops that involve multi-index arrays. The man page says (in section "Arrays"): [...] | The special operator in may be used to test if an array has an index | consisting of a particular value: | | if (val in array) | print array[val] | | If the array has multiple subscripts, use (i, j) in array. | | The in construct may also be used in a for loop to iterate over all the | elements of an array. [...] This made me think that I could write: for ((i, j) in array) print array[i, j] Unfortunately, this does not work! It seems that the other three possibilities work correctly: $ gawk 'BEGIN { array[42] = "answer"; if (42 in array) print array[42]; }' answer $ gawk 'BEGIN { array[42] = "answer"; for (val in array) print array[val]; }' answer $ gawk 'BEGIN { array[4,2] = "answer"; if ((4,2) in array) print array[4,2]; }' answer but iterating on multi-index arrays does not: $ gawk 'BEGIN { array[4,2] = "answer"; for ((i,j) in array) print array[i,j]; }' gawk: cmd. line:1: BEGIN { array[4,2] = "answer"; for ((i,j) in array) print array[i,j]; } gawk: cmd. line:1: ^ syntax error The man page does not clearly explain this. I found confirmation on this page: http://stackoverflow.com/questions/14280877/multidimensional-arrays-in-awk Please note that the reply also suggests a workaround for the missing feature. Is there any simpler or more elegant (but still portable to other AWK implementations, such as mawk) way to iterate on multi-index arrays? Please enhance the man page by clearly describing this unexpected behavior and (possibly) by suggesting a workaround. Please also forward this bug report upstream, if appropriate. Thanks for your time! -- System Information: Debian Release: jessie/sid APT prefers testing APT policy: (800, 'testing'), (500, 'unstable') Architecture: amd64 (x86_64) Kernel: Linux 3.10-3-amd64 (SMP w/2 CPU cores) Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/bash Versions of packages gawk depends on: ii libc6 2.17-93 ii libreadline6 6.2+dfsg-0.1 ii libsigsegv2 2.10-2 gawk recommends no packages. Versions of packages gawk suggests: pn gawk-doc <none> -- no debconf information
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--- Begin Message ---Version: 1:4.1.1+dfsg-1 Hello, Thanks for your bug report. I agree that the man page of gawk was unclear about for loops with multi-index arrays. Fortunately this has been clarified in the latest version: | The in construct may also be used in a for loop to iterate over all | the elements of an array. However, the (i, j) in array construct | only works in tests, not in for loops. The 'workaround' mentioned on the linked StackOverflow page is indeed the best way to iterate over multi-index arrays in Awk. The workaround is also documented in the Gawk manual [1], also available on Debian in the gawk-doc package. (Note that Gawk also has proper 'arrays of arrays' [2], but this is not portable to other Awk implementations). [1]: https://www.gnu.org/software/gawk/manual/html_node/Multi_002dscanning.html [2]: https://www.gnu.org/software/gawk/manual/html_node/Arrays-of-Arrays.html Regards, Jeroen Schot
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