JSON output using powershell in ForEach loop

Question

friends! Starting to work with powershell and encountered a problem. I need to output the values of some variables in a JSON format string in a loop. For this, I use the following code:

.....
    foreach ($value in $memoryLast5min)
    {
        $valueInt = [convert]::ToInt32($value, 10);   
        if ($valueInt -ge $500MB)
        {
            $index = [array]::IndexOf($memoryLast5min, $value);        
            $JSON += @{'problemUsers' = @(
                   @{
                        "userName"       = $userNames[$index]
                        "memoryLast5min" = $value
                        "readLast5min"   = $readLast5min[$index]
                        "writeLast5min"  = $writeLast5min[$index]
                    } 
                ) 
            } | ConvertTo-JSON;
        }
    }
.....
return $JSON

In the variable $JSON I get the following result:

{
    "problemUsers":  [
                         {
                             "userName":  "User1",
                             "writeLast5min":  29,
                             "memoryLast5min":  181,
                             "readLast5min":  25
                         }
                     ]
}{
    "problemUsers":  [
                         {
                             "userName":  "User2",
                             "writeLast5min":  80,
                             "memoryLast5min":  396,
                             "readLast5min":  74
                         }
                     ]
}{
    "problemUsers":  [
                         {
                             "userName":  "User3",
                             "writeLast5min":  32,
                             "memoryLast5min":  169,
                             "readLast5min":  29
                         }
                     ]
}

But I need this result:

{
    "problemUsers":  [
                         {
                             "userName":  "User1",
                             "writeLast5min":  29,
                             "memoryLast5min":  181,
                             "readLast5min":  25
                         },
                         {
                             "userName":  "User2",
                             "writeLast5min":  80,
                             "memoryLast5min":  396,
                             "readLast5min":  74
                         },
                         {
                             "userName":  "User3",
                             "writeLast5min":  32,
                             "memoryLast5min":  169,
                             "readLast5min":  29
                         }
                     ]
}

Please, help me fix the code

I’d try removing @{'problemUsers' = from your $json statement and the json conversion from your loop. Then outside of the loop do @{'problemUsers' = $json} | convertto-Json — AdminOfThings
– AdminOfThings, Commented Nov 6, 2019 at 15:27
@nzrytmn, my JSON file should look the same as in the 3rd code block of my question — himynameissergey
– himynameissergey, Commented Nov 6, 2019 at 15:37
@AdminOfThings thanks! It works! Outside of the loop do $JSON = @{'problemUsers' = $JSON} | convertto-Json — himynameissergey
– himynameissergey, Commented Nov 6, 2019 at 15:41

Tomalak · Accepted Answer · 2019-11-06 15:43:12Z

4

Build a data structure. When you're finished, convert to JSON.

$data = [pscustomobject]@{
    problemUsers = @()
}

foreach ($value in $memoryLast5min)
{
    $valueInt = [convert]::ToInt32($value, 10);   
    if ($valueInt -ge $500MB)
    {
        $index = [array]::IndexOf($memoryLast5min, $value) 
        $data.problemUsers += @{
            userName       = $userNames[$index]
            memoryLast5min = $value
            readLast5min   = $readLast5min[$index]
            writeLast5min  = $writeLast5min[$index]
        }
    } 
}

$json = $data | ConvertTo-Json

answered Nov 6, 2019 at 15:43

Tomalak

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4 Comments

Ansgar Wiechers Over a year ago

I think you need to create custom objects from the hashtables inside the loop too, and $data.problemUsers = @(foreach (...) {...}) would avoid appending to an array in a loop.

Tomalak Over a year ago

Custom objects and hash tables should work the same, am I missing something?

Ansgar Wiechers Over a year ago

No, you're right. I thought you needed objects, but I just checked and apparently hashtables work just the same.

Tomalak Over a year ago

I agree, $data.problemUsers = @(foreach (...) {...}) is more optimized for a single assignment, but then again, the OP might have more such sections where problem users are added based on different criteria, I did not want to preclude anything here.

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