PowerShell: How to Combine Multiple Hash Tables

Often you may want to combine multiple hash tables into a single hash table in PowerShell.

You can use the following methods to do so:

Method 1: Combine Hash Tables (With No Duplicate Keys)

$new_hash = $hash1 + $hash2

This particular example combines the hash tables named $hash1 and $hash2 into a new hash table named $new_hash.

This method works only if there are no duplicate keys between the two hash tables.

Method 2: Combine Hash Tables (With Duplicate Keys)

Function CombineHash([ScriptBlock]$Operator) {
    $Out = @{}
    ForEach ($h in $Input) {
        If ($h -is [Hashtable]) {
            ForEach ($Key in $h.Keys) {$Out.$Key = If ($Out.ContainsKey($Key)) {@($Out.$Key) + $h.$Key} Else {$h.$Key}}
        }
    }
    If ($Operator) {ForEach ($Key in @($Out.Keys)) {$_ = @($Out.$Key); $Out.$Key = Invoke-Command $Operator}}
    $Out
}

$hash1, $hash2 | CombineHash

This particular example creates a function named CombineHash that accepts a list of hash tables piped into it and combines the hash tables into a single hash table.

If there are duplicate keys between the hash tables, a single key will be shown in the combined hash table and the values will be added to an array.

Using this function, you can also use the $Operator parameter of the function to specify how to handle values from duplicate keys.

The following example shows how to use each method in practice.

Example 1: Combine Hash Tables (With No Duplicate Keys)

We can use the following code to combine two hash tables named $hash1 and $hash2 that contain no duplicate keys:

$hash1 = @{A=5; B=10; C=15}
$hash2 = @{D=20; E=25; F=30}

$new_hash = $hash1 + $hash2

The following screenshot shows how to use this syntax in practice:

The result is a single hash table named $new_hash that combines the values from both $hash1 and $hash2.

Example 2: Combine Hash Tables (With Duplicate Keys)

We can create the following function named CombineHash to combine hash tables together that may have duplicate keys:

Function CombineHash([ScriptBlock]$Operator) {
    $Out = @{}
    ForEach ($h in $Input) {
        If ($h -is [Hashtable]) {
            ForEach ($Key in $h.Keys) {$Out.$Key = If ($Out.ContainsKey($Key)) {@($Out.$Key) + $h.$Key} Else {$h.$Key}}
        }
    }
    If ($Operator) {ForEach ($Key in @($Out.Keys)) {$_ = @($Out.$Key); $Out.$Key = Invoke-Command $Operator}}
    $Out
}

We can then use the following code to create two hash tables that share some duplicate keys and use the CombineHash function to combine them into a single hash table:

$hash1 = @{A=5; B=10; C=15}
$hash2 = @{A=20; B=25; F=30}

$hash1, $hash2 | CombineHash

The following screenshot shows how to use this syntax in practice:

The combined hash table contains the values from both original hash tables, with values that share a key grouped into an array.

You could also use the following syntax to simply return the average value of duplicate keys:

$hash1 = @{A=5; B=10; C=15}
$hash2 = @{A=20; B=25; F=30}

$hash1, $hash2 | CombineHash {($_ | Measure-Object -Average).Average}

The following screenshot shows how to use this syntax in practice:

The value shown in the Value column now represents the average value between the duplicate keys.

Feel free to replace Average with Sum, Maximum, Minimum, etc. to return a different aggregate value instead.

Related Tutorials

The following tutorials explain how to perform other common tasks in PowerShell:

PowerShell: How to Check if Hash Table Contains Specific Key
PowerShell: How to Remove Elements from a Hash Table
PowerShell: How to Iterate Over a Hash Table
PowerShell: How to Update Values in Hash Table