Awk array iteration for multi-dimensional arrays

Question

Awk offers associative indexing for array processing. Elements of 1 dimensional array can be iterated:

e.g.

for(index in arr1)
  print "arr1[" index "]=" arr1[index]

But how this kind done for a two dimensional array? Does kind of syntax,given below work?

for(index1 in arr2)
for(index2 in arr2)
   arr2[index1,index2]     

Answer 1

No, the syntax

for(index1 in arr2) for(index2 in arr2) {
    print arr2[index1][index2];
}

won't work. Awk doesn't truly support multi-dimensional arrays. What it does, if you do something like

x[1,2] = 5;

is to concatenate the two indexes (1 & 2) to make a string, separated by the value of the SUBSEP variable. If this is equal to "*", then you'd have the same effect as

x["1*2"] = 5;

The default value of SUBSEP is a non-printing character, corresponding to Ctrl+\. You can see this with the following script:

BEGIN {
    x[1,2]=5;
    x[2,4]=7;
    for (ix in x) {
        print ix;
    }
}

Running this gives:

% awk -f scriptfile | cat -v
1^\2
2^\4

So, in answer to your question - how to iterate a multi-dimensional array - just use a single for(a in b) loop, but you may need some extra work to split up a into its x and y parts.

Answer 2

AWK fakes multidimensional arrays by concatenating the indices with the character held in the SUBSEP variable (0x1c). You can iterate through a two-dimensional array using split like this (based on an example in the info gawk file):

awk 'BEGIN { OFS=","; array[1,2]=3; array[2,3]=5; array[3,4]=8; 
  for (comb in array) {split(comb,sep,SUBSEP);
    print sep[1], sep[2], array[sep[1],sep[2]]}}'

Output:

2,3,5
3,4,8
1,2,3