Al wrote:
> I'm having trouble getting my head around the most basic of things about
> arrays, and wonder if anyone could post something very simple about
them,
> or point to some elementary link. I understand how to do the notation
as
> listed in Sed and Awk, or similar books. I can see it working when I
copy
> the formulae, but don't really understand why or how it works. What I
> don't get is sort of crazy, its 'what an array is'.
Basically an array is a collection of values of the same type[*] that are
ordered in a certain way or numbered (or named, in case of an associative
array) and whose elements can be accessed by that number (or name).
[*] You need additional concepts (like polymorphism or hybrid basic types)
to define arrays as inhomogenuous collections. And generally (non-awk'ish)
arrays can carry not only "values".
>
> Like, I have a file which goes something like this:
>
> 1 item1 2.99 sept
> 2 item2 4.25 may
>
> When you use the array commands to link the first column to the second,
as
I don't understand what you mean by "linked columns".
> shown in many of the examples, are you doing something like assigning
names
> in Excel? Is it a sort of view into the file?
Besides the conceptual view I described above an array is a technical tool
to memorize data; e.g. data in a file that you may need to store for later
usage.
Awk will read the file sequentially from the beginning and you can
instruct
awk to do certain tasks on each of the lines, like stripping only certain
fields ( {print $2, $4} ); that way you get something like a view on a
file.
Whenever you need to refer to previous data you have to store all
necessary
data in an array, though.
> If I'm trying to use the
> array commands to total, for instance, all sales of item1 in sept, am I
to
> create two views into the file....or?
You will instruct awk to consider only lines that match your "view" by
defining a pattern[**] $2=="item1" && $4=="sept" then define the action
to do on that files, summing up sum += $3 . Your program would be...
$2=="item1" && $4=="sept" { sum += $3 }
END { print sum }
So you don't need any arrays for this task since you store just a scalar
value (and not a collection of named/indexed elements).
[**] Assuming there's no whitespace in the second column (which awk used
as a field separator per default).
Janis
>
> I realize this is confused. Any basic help or pointers would be greatly
> appreciated.
>
> Peter
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