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 ahaystack. 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 ofneedles.
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 moduleinclude std/sequence.e--declare variablesobject needle1, needle2, needle3sequence haystack1, haystack2, haystack3sequence output1, output2, output3--initialize variableshaystack1 = {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 outputoutput1 = retain_all(needle1, haystack1)output2 = retain_all(needle2, haystack2)output3 = retain_all(needle3, haystack3)--print the output to displayprint(1,output1)puts(1,"\n")print(1,output2)puts(1,"\n")print(1,output3)puts(1,"\n")
Code explanation
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Line 2: We add a required module.
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Lines 5 to 7: We declare some variables.
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Lines 10 to 16: We assign values to the declared variables.
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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.
