Help to know the various possible uses of awk arrays


 
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# 1  
Help to know the various possible uses of awk arrays

Hi to all,

I write this time to ask for different syntax or ways of arrays within awk and uses.

Since I don't know how actually could work and the real potencial of awk arrays, I look for a proactive reply/help in order to get
more information than it seems I'm trying to get.

I think I have seen before in threads in this forum, solutions with different syntax used to load arrays, obviously
depending on the input file and what you want to do with it, the uses and syntax might vary.

*I show below only examples rescued from what I think I've seen, so some may have incorrect syntax.


Code:
{a[$1]=$2}
{a[k++]=$1}
{a[++i]=$3}
{a[i]=$3++}
{a[i]=++$3}
{++a[i]=$3}
{a[$2]=+$3}
{a[$4]++}

Summary:
1-) It would be fine the person who respond, could say which of those examples above has correct syntax, the meaning of expression
and what others possible syntax exist when we want to load an array from input file.
2-) After that, I'll try to play around/evaluate different syntax you can shared(multi dimensional too, if it possible) and test to see their
output (learning of that) when I apply them to a sample file like I put below.
3-) If you want to share some examples with arrays with the below input file, it would be great and very appreciated
(difference/multiplication between fields, totals, etc)Smilie!!!.
Code:
Product    Entry    Price($)    Purchased    Sold
Laptops    2010-05-20    50    25    10
Desktop Computers    2010-12-07    40    20    7
Printers    2010-09-12    30    37    12
Optical Mouse    2011-02-07    12    71    39
Monitor    2010-12-03    20    44    15
Batteries    2011-01-15    20    80    41
Ac Adapters    2011-03-14    17    31    11
Memories    2010-07-19    15    93    53
Hard Drives    2011-01-13    35    17    5
Totals


PS. It is not about a homework, it's about doubts that I have regarding handling arrays in awkSmilie

Many thanks in advance,

Regards.

Last edited by cgkmal; 03-21-2011 at 08:16 PM..
# 2  
Arrays in awk arrays are associative, indexed with char string, key-value pairs.
Code:
{a[$1]=$2} -- you are including the column 2 in an array 'a' indexed by $1 field
{a[k++]=$1} -- k must be a variable and you are incrementing the index value while storing field 1 in the array 'a'
{a[++i]=$3} -- same as above
{a[i]=$3++} -- in the array 'a' indexed by the value of i, you are storing the value of field 3 incremented by 1
{a[i]=++$3} -- same as above but pre-incremented
{++a[i]=$3} -- not sure on this 
{a[$2]=+$3} -- shorthand notation of a[$2]= a[$2]+$3, adding the values of the array 'a; indexed by column 2 with the column 3
{a[$4]++} -- this allows you to check the unique values stored in the array 'a', indexing through the field 4

Please correct me if I am wrong !!

Last edited by royalibrahim; 03-23-2011 at 03:33 AM..
# 3  
Hi royalibrahim,

Many thanks for your reply. I'm more clear with your answer. I still need to practice and practice more to handle this well.

Thanks again.Smilie

If somebody more has more examples or comments would be great!


Regards
 

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