AWK - Arrays

AWK has associative arrays and one of the best thing about it is - index need not to be continuous set of number; we can use either string or number as a array index. Also there is no need to declare the size of array in advance - array can expand/shrink at runtime. This tutorial describe the AWK arrays with suitable examples.

Below is the syntax of the array:

array_name[index]=value

Where array_name is the name of array, index is the array index and the value is any value assigning to the element of the array.

Creation

To gain insights about array let us create and access the elements of the array.

[jerry]$ awk 'BEGIN {
fruits["mango"]="yellow";
fruits["orange"]="orange"
print fruits["orange"] "\n" fruits["mango"]
}'

On executing the above code, you get the following result:

orange
yellow

In above example we have declared array namely fruits whose index is fruit name and value is colour of the fruit. To access array element we have used array_name[index] format.

Deletion

For insertion we used assignment operator. Similarly we can use delete statement to remove an element from the array. Below is the syntax of delete statement:

delete array_name[index]

Below example deletes element orange hence command does not show any output.

[jerry]$ awk 'BEGIN {
fruits["mango"]="yellow";
fruits["orange"]="orange";
delete fruits["orange"];
print fruits["orange"]
}'

Multi-dimensional arrays

Awk only supports single dimensional arrays. But we can easily simulate a multi-dimensional array using the single dimensional array itself.
For instance below is 3x3 three-dimensional array:

100 200 300
400 500 600
700 800 900

In above example array[0][0] stores 100, array[0][1] stores 200 and so on. To store 100 at array location [0][0] we can use following syntax:

array["0,0"] = 100

Though we have given 0,0 as index, these are not two indexes. In reality it's just one index with the string 0,0.
Below simple example simulates 2-D array:

[jerry]$ awk 'BEGIN {
array["0,0"] = 100;
array["0,1"] = 200;
array["0,2"] = 300;
array["1,0"] = 400;
array["1,1"] = 500;
array["1,2"] = 600;
# print array elements
print "array[0,0] = " array["0,0"];
print "array[0,1] = " array["0,1"];
print "array[0,2] = " array["0,2"];
print "array[1,0] = " array["1,0"];
print "array[1,1] = " array["1,1"];
print "array[1,2] = " array["1,2"];
}'

On executing the above code, you get the following result:

array[0,0] = 100
array[0,1] = 200
array[0,2] = 300
array[1,0] = 400
array[1,1] = 500
array[1,2] = 600

We can also perform variety of operations on the array- like sorting its elements/indexes. For that purpose we can use AWK's asort and asorti function. We will see usage of these functions in latter chapter.