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Iterating over a list for comparing it with another list

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Posted on by Antonioclk

Hello,

i have two lists A and B. I need to check if all elements of A are present in B, and remove the elements that are not present in B.

In normal programming i would use a while or for loop to iterate over each item and check if it exists in list B, how should i do in power apps???

thank you so much

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Building Power Apps

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v-qiaqi@microsoft.com on at

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Hi @Antonioclk,

Could you please tell me if there is primary key between listA and listB?

If there is a column like ID existing in listA and listB, you could add a Gallery and set its Items property as:

Filter(listA,ID in listB.ID)

This will display elements of A are present in B.

To remove the elements are not present in B, you could add a butto and set OnSelect:

RemoveIf(ListA,!(ID in ListB.ID))

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Antonioclk on at

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thanks for the quick answer... actually there is no ID.
List A has only a Value column with elements like "soccer, cooking, reading".
List B has several columns, and the one that interest me is "Skill" column, which have elements like "soccer, cooking" but has less skills than the ones in list A.
I need to remove the elements of A that are not present in B.

Basically it's a migration from an old db, where the list of skills had more elements, to a newer list where there are less elements. I want to remove entries that are not in the list anymore
in power apps i get lost on how to do such operations that normally would require a for or while loop 😄

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v-qiaqi@microsoft.com on at

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Hi @Antonioclk,

In Power Apps, this Filter() function does loop through both lists, however, if there is a primary key, it is hard to iterate.

The reason why we need a id column is that we need a unique column to compare with the one in listB so that we could capture the record easily.

There is a function ForAll() to loop through the records in a table.

ForAll function in Power Apps - Power Platform | Microsoft Learn

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Antonioclk on at

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I basically have an old list of skills on the db. The new dropdown, has fewer skills, so i want to remove from the db all the items that are not in the dropdown anymore.

I just cleaned the code to simplify... i now have
CollectionA (the old list from the db) with only the Value column and inside there's "soccer, cooking, reading, swimming, programming"
CollectionB (the correct list that is used as reference to compare and remove) with only the Skill column and inside there's "soccer, swimming, cooking, yoga"
i should have a new list (or fix the CollectionA) that would show just "soccer, cooking, swimming".

I placed the two lists insde 2 tables and they are shown correctly,
then i tried to make a new table with this code, but it doesn't work. it shows an error on the tmpCurrentSkillsList.Value, why?

Filter(collectionA, Value in CollectionB.Skill)

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Antonioclk on at

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i changed syntax and used
Filter(collectionA, Value in CollectionB)
and showed no errors, but still it's not correct.

as you can see from the picture, the first list, has more elements that should be added in the filter, for instance Power App or Power Automate... but the filtered list only shows one element

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v-qiaqi@microsoft.com on at

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Hi @Antonioclk,

I am back to my office now, a new day.😂

I will test it later and responde here to update...

UPDATE

To check if all the records from ListA existing in ListB, I have a simple demo for your reference.

1). colA has a column named Title, colB has a column named Title.

2). Only1,2,5 from colA exist in colB, so based on your need, you just want to list 1,2,5 in the Gallery and remove 3,4,Tues from colA, right?

3). To delete the elements not existing in colB, you just need to use the RemoveIf():

RemoveIf(colA,!(Title in colB.Title))

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