What is the retain_all() method in Euphoria?

Overview

The retain_all() method is used to manipulate Euphoria sequences. This method will remove all the elements of a haystack sequence except for those present in the needle sequence.

Syntax

retain_all(needles,haystack)

Parameters

  • needles: This is the set of elements to be retained if found in a haystack. It is a data type object and it is a required parameter.

  • haystack: This is the sequence containing elements that will be removed if not found as part of needles.

Return value

This method returns a new sequence that contains only those elements from haystack that are also in needles. An empty sequence will be returned if none of the elements of needles are found in haystack.

Code example

Let’s look at the code below:

--add a required module
include std/sequence.e
--declare variables
object needle1, needle2, needle3
sequence haystack1, haystack2, haystack3
sequence output1, output2, output3
--initialize variables
haystack1 = {1,2,4,5,6,7}
haystack2 = {8,9,10,11,12,17}
haystack3 = {20,30,40,50}
needle1 =  {3,4}
needle2 =  {8,9,10,17}
needle3 = {80,90}
--call the retain_all() method and save its output
output1 = retain_all(needle1, haystack1)
output2 = retain_all(needle2, haystack2)
output3 = retain_all(needle3, haystack3)
--print the output to display
print(1,output1)
puts(1,"\n")
print(1,output2)
puts(1,"\n")
print(1,output3)
puts(1,"\n")

Code explanation

  • Line 2: We add a required module.

  • Lines 5 to 7: We declare some variables.

  • Lines 10 to 16: We assign values to the declared variables.

  • Lines 18 to 20: We call the retain_all() method and store the resulting sequences in output variables.

  • Line 22 to 27: We print all the output variables.

Output

The output in line 27 is an empty sequence ({}) because none of the needles in variable needle3 are found in the haystack parameter, haystack3. Therefore, there is nothing to retain.

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