[H-GEN] one for an awk guru

[Mark J. Suter]

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On Wed, 4 Feb 1998, Michael Dooley wrote:

>             Here's something strange I've seen with awk and nawk a
> couple of time now.  In this case I'm finding lines from headers of
> files where $1 is SSBOND and creating an array of $4's and $6's.  Here's
> some sample lines:

[ snip ]
 
> If I use the alternative 'for' definition : for (m=1;m<=x;m++), I get
> the output I want.  However x will vary from file to file so I'd rather
> use the array specification of for.
> 
> Is this a case of the script giving me what I ask for, not what I want
> (??!!) any ideas?

Benjamin Carlyle's explanation about hash-tables was correct, from a
certain point of view.  The hash-tables are an implementation issue.
The true source of the lack of ordering lies in the nature of the
arrays, not how they are stored.

Arrays in awk are different from those in most other programming
languages, such as C: they are associative.  With an associative array,
order is irrelevant!  Thus, hash-tables which don't preserve order
are a suitable means of storing a data structure for which order
is unimportant.

The `for e in array' construct is used to iterate over the entire
array, without regard to order, as is appropriate for an associative
array.

For more detail, see the documentation for a explanation of gawk's
associative arrays at http://www.tec.ualberta.ca/Documentation
/Info/by-chapter/gawk-3.0.3/gawk_12.html

Yours sincerely,

Mark Suter.

- -- Mark John Suter | I know that you  believe  you understand
suter at humbug.org.au  | what you think I said, but I am not sure
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Ph: +61 7 3891 2085  | what I meant.                  anonymous

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