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How to sum values from one Sharepoint list to another based on unique value.

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Posted on by twoods

Looking for a bit of guidance on setting up a flow to sum values from one SharePoint list to another based on unique identifier.

Scenario

I have ListA that contains an inventory of items and quantity purchased. The Title (single line of text) field will be a unique name in this list, with the Quantity purchased field being a Number field.

ListA Example:

Title	Quantity Purchased	Quantity Used
Item1	50
Item2	25

ListB contains a list of the items and the quantities used. Again with Title being a single line of text, and the Quantity Used being a number

ListB Example:

Title	Quantity Used
Item1	10
Item2	5
Item1	10
Item1	10

The end goal would be to sum the values for each item from ListB (when a new item is added to the list) and update the corresponding items Quantity Used field in ListA.

ListA After flow has ran:

Title	Quantity Purchased	Quantity Used
Item1	50	30
Item2	25	5

Thank you,

Categories:

Building flows

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v-LilyW-msft on at

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Hi @twoods
I set up a flow, you can take a try with the screenshots below to see if it helps.
Here are my two lists.
Flow in details.
Expression:
union(array(items('Apply_to_each')?['Title']),variables('Title'))
Expression:
int(items('Apply_to_each_3')?['QuantityUsed'])
Save and test the flow.
After flow runs, List A will be update like below.
Hope the content above may help you.
Best Regards
If my solution helps, then please consider Accept it as the solution to help the other members find it more quickly.

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cd-lyst 4 on at

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Hello, thank you for the post. I am trying to complete something very similar but am struggling to get past the finish line.

Please disregard, it looks like I fixed it! 🙂

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Juan2004 8 on at

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Hello, I'm having the same problem that you had. How did you manage to fix it?

Thanks.
-Juan

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cd-lyst 4 on at

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In my SharePoint list, I'm using a decimal number so I have to use FLOAT here in Power Automate. The post says to use INT but that isn't compatible with decimals, which is why Compose 2 was throwing the error.

Not sure if this helps but I had to add a few helper columns in the SP list to get the proper columns updated (i.e. run a calculated column and have it be updated to a text/number column in the same Flow).

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newbiepowernow 2 on at

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hi, can you kindly clarify what are the Title's in the first Compose expression?

union(array(items('Apply_to_each')?['Title']),variables('Title'))

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cd-analyst 2 on at

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Hello, this is just a variable that you create earlier in the steps.

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FredCongo 2 on at

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Hello, I tryied this exemple
But the update for 'apply to each 4' is not working.
Someone can tell me why ?

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Ellis Karim 11,681 Super User 2025 Season 2 on at

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Here is an alternative method for summing the values of an array using XML:

Expressions used in the flow:

{ "root": { "number": @{body('Select')} } } xpath(xml(outputs('Compose_JSON')), 'sum(/root/number)')

For more information on this method see : Instantly sum an array with Power Automate (tachytelic.net)

Ellis

https://elliskarim.com

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trice602 15,402 Super User 2025 Season 2 on at

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I also like the xpath approach here and is also a viable solution. Tom

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Chriddle 8,436 Super User 2025 Season 2 on at

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Just one expression using xpath:

From: @{outputs('ListA')}

Map:

addProperty( item(), 'QuantityUsed', xpath( xml(json(concat('{"Root":{"Item":', outputs('ListB'), '}}'))), concat('sum(//Item[Title="', item()['Title'], '"]/QuantityUsed)') ) )

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