Awk from entry to earth (8) array

Array

AWK There are data structures like associative arrays , The best feature of this data structure is that its index value does not need to be a continuous integer value . We can use both numbers and strings as the index of the array . besides , Associative arrays do not need to declare their size in advance , Because it can automatically increase or decrease at run time . This chapter will explain AWK How to use arrays .

The following is the syntax format used by the array ：

array_name[index]=value

among array_name Is the name of the array ,index Is the array index ,value The value assigned to the element in the array .

Create array

To learn more about arrays , Let's first look at how to create an array and how to access array elements ：

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

Execute the above command to get the following result ：

orange
yellow

In the example above , We define a fruit (fruits) Array , The index of this array is the fruit name , Value is the color of the fruit . You can access array elements in the following format ：

array_name[index] 

Delete array elements

When inserting elements, we use assignment operators . When deleting array elements , We use delete sentence . As shown below ：

delete array_name[index]

In the following example , Array orange The element is deleted （ The delete command has no output ）：

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

Multidimensional arrays

AWK Itself does not support multidimensional arrays , However, we can easily use one-dimensional array simulation to realize multi-dimensional array .

The following example is a 3x3 Three dimensional array of ：

100 200 300
400 500 600
700 800 900

In the example above ,array[0][0] Storage 100,array[0][1] Storage 200 , By analogy . In order to be in array[0][0] Store 100, We can use the following syntax ：

array["0,0"] = 100

Although in the example , We used 0,0 As index , But these are not two index values . in fact , It is a string index 0,0.

The following is an example of simulating a two-dimensional 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"];
}'

You can get the following result by executing the above command ：

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

Many operations can be performed on arrays , such as , Use asort Finish sorting array elements , Or use asorti Implement the sorting of array index, etc . We will introduce functions that can operate on arrays in later chapters .