Powershell - issue with matching an object within a list with another object within another list of object

If I understand you correctly, if an object in A matches the 3 properties of an object in list b then you will check OtherData2 and return the object depending on that check. If it's not in list b then just return the object. I've created some sample data for this demonstration.

$lista = @'
[
    {
        "computerName": 123,
        "userName": "john",
        "otherData1": "data128",
        "otherData2": "yyy"
    },
    {
        "computerName": 456,
        "userName": "joan",
        "otherData1": "data821",
        "otherData2": "nnn"
    },
    {
        "computerName": 789,
        "userName": "doug",
        "otherData1": "data111",
        "otherData2": "abc"
    }
]
'@

$listb = @'
[
    {
        "computerName": 123,
        "userName": "john",
        "otherData1": "data128",
        "otherData2": "yyy"
    },
    {
        "computerName": 789,
        "userName": "doug",
        "otherData1": "data111",
        "otherData2": "abc"
    }
]
'@

$listObjA = $lista | ConvertFrom-Json
$listObjB = $listb | ConvertFrom-Json

foreach($objA in $listObjA)
{
    if($listObjB | where {$_.computername -eq $objA.computername -and
                          $_.username -eq $objA.username -and
                          $_.otherData1 -eq $objA.otherdata1})
    {
        if($objA.otherdata2 -eq 'yyy')
        {
            $objA
        }
    }
    else
    {
        $objA
    }
}

The output will be 2 objects from list a, one that was in list b AND otherdata2 met the criteria and the other was not in list b.

computerName userName otherData1 otherData2
------------ -------- ---------- ----------
         123 john     data128    yyy       
         456 joan     data821    nnn   

Edit

Ok, first issue you're going to face is combining of the different JSON files that contain arrays. See the following test.

$listb1 = New-TemporaryFile
$listb2 = New-TemporaryFile

@'
[
    {
        "computerName": "789",
        "userName": "Cyril",
        "otherData1": "file2.pps",
        "otherData2": "yyy"
    },
    {
        "computerName": "321",
        "userName": "Damien",
        "otherData1": "doc.docx",
        "otherData2": "bbb"
    }
]
'@ | Set-Content $listb1 -Encoding UTF8

@'
[
    {
        "computerName": "123",
        "userName": "Antoine",
        "otherData1": "test1.xls",
        "otherData2": "yyy"
    },
    {
        "computerName": "123",
        "userName": "Antoine",
        "otherData1": "test2.xls",
        "otherData2": "yyy"
    }
]
'@ | Set-Content $listb2 -Encoding UTF8

$listObjB = $listb1,$listb2 | foreach {Get-content $_ -Raw | ConvertFrom-Json}

$listObjB.Count

2

You end up with 2 arrays of 2 objects, surely not what you were expecting. However, by simply putting a subexpression around the get-content | convert command, powershell will unroll those into individual items. See this excellent answer by the other commenter Maximillian Burszley for more info.

$listObjB = $listb1,$listb2 | foreach {(Get-content $_ -Raw | ConvertFrom-Json)}

$listObjB.Count

4

That's what we were expecting. We will need to apply the same to the obja list

$lista1 = New-TemporaryFile
$lista2 = New-TemporaryFile

@'
[
    {
        "computerName": "123",
        "userName": "Antoine",
        "otherData1": "test1.xls",
        "otherData2": "yyy"
    },
    {
        "computerName": "123",
        "userName": "Antoine",
        "otherData1": "test2.xls",
        "otherData2": "yyy"
    },
    {
        "computerName": "456",
        "userName": "Benoit",
        "otherData1": "file1.txt",
        "otherData2": "yyy"
    }
]
'@ | Set-Content $lista1 -Encoding UTF8

@'
[
    {
        "computerName": "789",
        "userName": "Cyril",
        "otherData1": "file1.pps",
        "otherData2": "yyy"
    },
    {
        "computerName": "789",
        "userName": "Cyril",
        "otherData1": "file2.pps",
        "otherData2": "yyy"
    },
    {
        "computerName": "321",
        "userName": "Damien",
        "otherData1": "doc.docx",
        "otherData2": "yyy"
    }
]
'@ | Set-Content $lista2 -Encoding UTF8

$listobjA = $lista1,$lista2 | foreach {(Get-content $_ -Raw | ConvertFrom-Json)}

Then make a slight change to my suggested solution

foreach($objA in $listobjA)
{
    if($matchedobj = $listObjB | where {$_.computername -eq $objA.computername -and
                          $_.username -eq $objA.username -and
                          $_.otherData1 -eq $objA.otherdata1})
    {
        if($objA.otherdata2 -ne $matchedobj.otherData2)
        {
            $objA
        }
    }
    else
    {
        $objA
    }
}

And we will end up with the expected results.

computerName userName otherData1 otherData2
------------ -------- ---------- ----------
456          Benoit   file1.txt  yyy       
789          Cyril    file1.pps  yyy       
321          Damien   doc.docx   yyy       

You could also do the a conversion as part of the loop like this.

foreach($objA in $lista1,$lista2 | foreach {(Get-content $_ -Raw | ConvertFrom-Json)})
{
    if($matchedobj = $listObjB | where {$_.computername -eq $objA.computername -and
                            $_.username -eq $objA.username -and
                            $_.otherData1 -eq $objA.otherdata1})
    {
        if($objA.otherdata2 -ne $matchedobj.otherData2)
        {
            $objA
        }
    }
    else
    {
        $objA
    }
}

But I personally feel the former was easier to read and understand.