Append dictionary to a dictionary in powershell (hashtable) - powershell

Question

I have two dictionaries like this:
$first = #{}
$first.Add('John', 'Doe')
$first.Add('Johnny', 'Doe')
$second = #{}
$second.Add('Jack', 'Test')
$second.Add('Jacky', 'Test')
And I have a general $all = #{} dictionary, that stands for all dictionaries combined.
Ex. when I want to see all keys that $all contains:
foreach($key in $all){
Write-Host $key
}
It will show this:
John
Johnny
Jack
Jacky
p.s. I have this one:
$all = #{}
$all_dict = #{}
$all_dict += $first
$all_dict += $second
foreach($dict in $all_dict){
foreach($key in $dict.Key){
$all.Add($key, $dict[$key])
}
}
But I was wondering if there is another way to do it without the need to add all dictionaries to an array and then iterate through them

Answer 1

I wouldn't do the += addition to hashtables, but instead use a ForEach-Object on the hashes .Keys. That way, the code can be shortened, but also it will leave you an easier choice whether you would want the possible duplicates from Hashtable 1 ($first) to be overwritten by the values from the second Hashtable ($second).
Something like this:
$first = #{}
$first.Add('John', 'Doe')
$first.Add('Johnny', 'Doe')
$second = #{}
$second.Add('Jack', 'Test')
$second.Add('Jacky', 'Test')
$second.Add('Johnny', 'Depp') # Duplicate key: same first name, different lastname
$all = #{}
# copy all keys and values from the $first Hashtable into $all
$first.Keys | ForEach-Object { $all[$_] = $first[$_] }
For the next part, you'll have to decide what to do with duplicate keys:
Method 1
# add the stuff from Hashtable $second to it:
# this will overwrite the value if the key already exists (i.e. $second value 'wins')
$second.Keys | ForEach-Object { $all[$_] = $second[$_] }
OR use Method 2
# make sure the value of the $first hashtable is NOT overwritten (i.e. $first value 'wins')
$second.Keys | ForEach-Object { if (!($all.ContainsKey($_))) { $all[$_] = $second[$_] }}
In case you choose to overwrite (method 1), the $all hash will contain
Name Value
---- -----
John Doe
Jacky Test
Johnny Depp
Jack Test
If you choose NOT to overwrite (method 2), $all will be
Name Value
---- -----
John Doe
Jacky Test
Johnny Doe
Jack Test
Edit
There is another approach where you rely on the fact that an exception is thrown if you try to add an entry that already exists. In that case, use the .Add(key, value) method and wrap it inside a try{..} catch{..} block.
Without that catch, the error prevents the $all Hashtable to be filled, as it stops at the first duplicate key you try to add.
$second.Keys | ForEach-Object {
try {
$all.Add($_, $second[$_])
}
catch {
# catch the exception in order to carry on adding items
# the effect will be that the values from $first will not be overwritten
# just like with method 2
Write-Warning $_.Exception.Message
}
}

Answer 2

I think your $all_dict already contains what you want (i.e. a hashtable with all 4 entries), but your foreach( $dict in $all_dict ) isn't enumerating the hashtable entries like you expect it to.
The quick answer is to iterate over the Keys collection instead:
foreach( $key in $all.Keys )
{
write-host $key
}
The longer answer is that in your example PowerShell is doing some "helper" things for you with enumeration - foreach($key in $all) is only enumerating over a single object ($all), but write-host $all is evaluating an array of all of the entries in $all and serializing them into a single string:
Compare the behaviour of these two lines and you can see the difference:
PS> foreach($item in #{ "aaa"="bbb"; "ccc"="ddd" }) { write-host $item }
System.Collections.DictionaryEntry System.Collections.DictionaryEntry
PS> foreach($item in #{ "aaa"="bbb"; "ccc"="ddd" }.Keys) { write-host $item }
ccc
aaa
By the way, watch out for if your keys collide - if you try #{ "aaa"="bbb"; "ccc"="ddd" } + #{ "aaa"="eee" } for example, you'll get an error Item has already been added. Key in dictionary: 'aaa' Key being added: 'aaa'. so you might want to find a better way to merge your hashtables rather than just using +.

Answer 3

Am I not understanding the question? You can add them.
$first = #{John = 'Doe'; Johnny = 'Doe'} # hashtables
$second = #{Jacky = 'Test'; Jack = 'Test'}
$all = $first + $second # merge two hashtables
foreach ($i in $all.getenumerator()) { $i } # loops 4 times