Compare two lists in Power Automate without loops

The challenge

List A has every customer in your Customers table. List B has customers who are already subscribed to your newsletter. You need the customers in List A whose email address is not in List B.

[
  { "FirstName": "Orlando", "LastName": "Gee", "EmailAddress": "[email protected]" },
  { "FirstName": "Keith", "LastName": "Harris", "EmailAddress": "[email protected]" },
  { "FirstName": "Donna", "LastName": "Carreras", "EmailAddress": "[email protected]" },
  { "FirstName": "Janet", "LastName": "Gates", "EmailAddress": "[email protected]" },
  { "FirstName": "Lucy", "LastName": "Harrington", "EmailAddress": "[email protected]" }
]

[
  { "FirstName": "Keith", "LastName": "Harris", "EmailAddress": "[email protected]" },
  { "FirstName": "Janet", "LastName": "Gates", "EmailAddress": "[email protected]" },
  { "FirstName": "Lucy", "LastName": "Harrington", "EmailAddress": "[email protected]" }
]

The answer should be Orlando Gee and Donna Carreras — or rather, their email addresses; the last step below explains why that distinction matters.

Before you start

Every action below can be pasted in directly: add the action, open its ··· menu › Peek code, and paste. Power Automate keeps the action’s position (and runAfter) from wherever you dropped it, so add each one in order and only paste over its type/inputs.

• Add two Compose actions named List A and List B, then peek-code-paste these:

{
  "type": "Compose",
  "inputs": [
    { "FirstName": "Orlando", "LastName": "Gee", "EmailAddress": "[email protected]" },
    { "FirstName": "Keith", "LastName": "Harris", "EmailAddress": "[email protected]" },
    { "FirstName": "Donna", "LastName": "Carreras", "EmailAddress": "[email protected]" },
    { "FirstName": "Janet", "LastName": "Gates", "EmailAddress": "[email protected]" },
    { "FirstName": "Lucy", "LastName": "Harrington", "EmailAddress": "[email protected]" }
  ]
}

{
  "type": "Compose",
  "inputs": [
    { "FirstName": "Keith", "LastName": "Harris", "EmailAddress": "[email protected]" },
    { "FirstName": "Janet", "LastName": "Gates", "EmailAddress": "[email protected]" },
    { "FirstName": "Lucy", "LastName": "Harrington", "EmailAddress": "[email protected]" }
  ]
}

• The same steps work for any two arrays of objects with an EmailAddress field, such as two Dataverse List rows actions or two SharePoint Get items actions.
• No premium license is needed: every action here is a built-in data operation.

The solution

Two Compose actions hold the test data. Two Select actions and one Filter array do the actual comparison — no loops.

123

1. Compose actions hold the List A and List B test data.
2. Two Select actions turn each customer's email address into a string.
3. Filter array keeps the List A emails that List B does not contain.

How it works

• string(item()?['EmailAddress']) pulls the email out of each row and converts it to plain text; wrapping it in string() turns a missing property into "" instead of null, which the Filter array condition can’t compare against.
• Filter array checks each List A email, item(), against the List B emails, and does not contain keeps the ones List B doesn’t have.
• List A goes in From because it’s the list being filtered. List B, the smaller list, is only searched.
• The output is a list of email addresses, not customer objects — the Select actions already stripped everything else away.

Variations

• Items in both lists: change the operator to contains.
• Items in List B that are not in List A: swap them. Put the Select From List B output in From and the Select From List A output on the left.
• Compare whole rows instead of one column: map string(item()) in both Select actions instead of pulling out EmailAddress. Use this when the two lists don’t share a reliable key column — but see the gotcha below first.
• Get the full customer record back, not just the email: add a second Filter array after this one, with From set to the original List A output (outputs('List_A')) and the condition contains(body('Filter_array'), item()?['EmailAddress']). That looks up the full row for each matching email.
• Ignore upper and lower case: wrap the expression in toLower(...), e.g. toLower(string(item()?['EmailAddress'])).

Gotchas

• Matching is case-sensitive. “Ana” and “ana” are different strings.
• The Filter array output is email addresses only. If a later step needs the customer’s name or other fields, use the “get the full record back” variation above rather than trying to parse the email string.