powershell foreach nested array not showing expected output

Question

I don't understand why it loops badly.

$a = @("server1", "server2", "server3")
$b = @(121, 453, 565)
foreach ($element in $a) {
  foreach ($element2 in $b) {
    Write-Host $element " load is: " $element2
  } 
}

Output:

server1  load is:  121
server1  load is:  453
server1  load is:  565
server2  load is:  121
server2  load is:  453
server2  load is:  565
server3  load is:  121
server3  load is:  453
server3  load is:  565

I expect the following output:

server1 load is: 121
server2 load is: 453
server3 load is: 565

I don't understand how can I fix it. Thanks!

Because you have a foreach loop inside a foreach loop, hence 3 * 3 = 9 lines. — C. Helling
– C. Helling, Commented Nov 10, 2017 at 15:27
So I should use a for loop instead. Thank you very much. It makes sense. — catalin
– catalin, Commented Nov 10, 2017 at 15:32

C. Helling · Accepted Answer · 2017-11-10 15:32:29Z

2

You have a foreach loop inside a foreach loop, hence you're getting 3 * 3 = 9 lines.

The correct way to do what you want is to refer to the array by index.

$a = @("server1", "server2", "server3")
$b = @(121, 453, 565)
for ($i=0; $i -lt $a.length; $i++) 
{ 
  write-host $a[$i] load is: $b[$i] 
}

answered Nov 10, 2017 at 15:32

C. Helling

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Comments

Matt · Accepted Answer · 2017-11-10 16:44:55Z

You have a 3 element loop nested inside a 3 element loop hence why you are getting 9 results. What you want to do is step through both arrays simultaneously.

$a = @("server1", "server2", "server3")
$b = @(121, 453, 565)

for($index = 0; $index -lt $a.Count;$index++){
    Write-Host "$($a[$index]): $($b[$index])"
}

or

0..($a.Count - 1) | Foreach-Object{
    Write-Host $a[$_]: $b[$_]
}

Both of those solutions assume that $a and $b have the same number of elements. By default requesting a non-existent is not an error in PowerShell. A $null would be returned.

For how you are treating these you would be better of with at minimum a hashtable. This would be structured better and remove some potential failure points. Then you can iterate over each key value pair in one loop

$a = @{
    "server1"= 121
    "server2"= 453
    "server3"= 565
}

$a.GetEnumerator() | ForEach-Object{
    Write-Host $_.Key": " $_.value
}

Esperento57 · Accepted Answer · 2017-11-11 20:28:45Z

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