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8.2 The delete
Statement
To remove an individual element of an array, use the delete
statement:
delete array[index-expression] |
Once an array element has been deleted, any value the element once had is no longer available. It is as if the element had never been referred to or been given a value. The following is an example of deleting elements in an array:
for (i in frequencies) delete frequencies[i] |
This example removes all the elements from the array frequencies
.
Once an element is deleted, a subsequent for
statement to scan the array
does not report that element and the in
operator to check for
the presence of that element returns zero (i.e., false):
delete foo[4] if (4 in foo) print "This will never be printed" |
It is important to note that deleting an element is not the
same as assigning it a null value (the empty string, ""
).
For example:
foo[4] = "" if (4 in foo) print "This is printed, even though foo[4] is empty" |
It is not an error to delete an element that does not exist.
However, if ‘--lint’ is provided on the command line
(see section Command-Line Options),
gawk
issues a warning message when an element that
is not in the array is deleted.
All the elements of an array may be deleted with a single statement
(c.e.)
by leaving off the subscript in the delete
statement,
as follows:
delete array |
This ability is a gawk
extension; it is not available in
compatibility mode (see section Command-Line Options).
Using this version of the delete
statement is about three times
more efficient than the equivalent loop that deletes each element one
at a time.
The following statement provides a portable but nonobvious way to clear out an array:(37)
split("", array) |
The split()
function
(see section String-Manipulation Functions)
clears out the target array first. This call asks it to split
apart the null string. Because there is no data to split out, the
function simply clears the array and then returns.
CAUTION: Deleting an array does not change its type; you cannot delete an array and then use the array’s name as a scalar (i.e., a regular variable). For example, the following does not work:
a[1] = 3 delete a a = 3
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