PowerShell - ConvertTo-Json how to get ndjson result

Question

I am trying to split 1 NDJSON file into multiple NDJSON files. I am able to consume and split the file, but the problem is the resulting files are in JSON format. Is it possible to output to NDJSON format or do I have to do some string manipulation?

My input file test.json:

{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38116"}

My powershell script so far:

$json = (Get-Content C:\Temp\test.json) | ConvertFrom-Json

$jnl_list = $json.JRNAL_NO | select -Unique

ForEach ($jnl in $jnl_list) {
    $Array = $json | Where-Object {$_.JRNAL_NO -eq $jnl}
    $res = ($Array | ConvertTo-Json)    
    $res | Out-File -FilePath .\JNL\$($jnl).json   
}

My current output. Here's the 38115.json file:

[
    {
        "PERIOD":  "2024004",
        "JRNAL_NO":  "38115"
    },
    {
        "PERIOD":  "2024004",
        "JRNAL_NO":  "38115"
    },
    {
        "PERIOD":  "2024004",
        "JRNAL_NO":  "38115"
    },
    {
        "PERIOD":  "2024004",
        "JRNAL_NO":  "38115"
    }
]

I need the output file to be NDJSON, basically the same format as the input file. 38115.json should be:

{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38115"}

38116.json should be:

{"PERIOD":"2024004","JRNAL_NO":"38116"}

Answer 1

If I understand correctly what you're looking for, the code my be greatly simplified by using Group-Object.

To get the NDJSON format what you can do is enumerate each object from the group of objects (.Group property) and pass it to ConvertTo-Json -Compress then send that output to your file.

$json = Get-Content C:\Temp\test.json | ConvertFrom-Json
foreach ($group in $json | Group-Object JRNAL_NO) {
    $group.Group |
        ForEach-Object { $_ | ConvertTo-Json -Compress } |
        Set-Content ".\JNL\$($group.Name).json"
}

Code above with the sample data would be creating 2 files:

• 38115.json

{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38115"}
{"PERIOD":"2024004","JRNAL_NO":"38115"}

• 38116.json

{"PERIOD":"2024004","JRNAL_NO":"38116"}