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

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

You can, however, iterate over a numerically indexed array using nested for loops:

for (i = 1; i <= width; i++)
    for (j = 1; j < = height; j++)
        print array[i, j]

Another noteworthy bit of information from the GAWK manual:

To test whether a particular index sequence exists in a multidimensional array, use the same operator (in) that is used for single dimensional arrays. Write the whole sequence of indices in parentheses, separated by commas, as the left operand:

if ((subscript1, subscript2, ...) in array)
   ...

Gawk 4 adds arrays of arrays. From that link:

for (i in array) {
    if (isarray(array[i])) {
        for (j in array[i]) {
            print array[i][j]
        }
    }
    else
        print array[i]
}

Also see Traversing Arrays of Arrays for information about the following function which walks an arbitrarily dimensioned array of arrays, including jagged ones:

function walk_array(arr, name,      i)
{
    for (i in arr) {
        if (isarray(arr[i]))
            walk_array(arr[i], (name "[" i "]"))
        else
            printf("%s[%s] = %s\n", name, i, arr[i])
    }
}