Using Powershell, how can i count the occurrence of each element in an array?

Question

If I have an array:

1 1 1 2 2 3 4 4 4 4 5 5

How can I use Powershell to tell me how many of each element there are in that array?

To be a little more clear, I should have a separate count for each array element:

Element:Count

1:3

2:2

3:1

4:4

5:2

Joey · Accepted Answer · 2012-09-28T14:10:34.133

36

You can use the Group-Object cmdlet:

PS> 1,1,1,2,2,3,4,4,4,4,5,5 | group

Count Name                      Group
----- ----                      -----
    3 1                         {1, 1, 1}
    2 2                         {2, 2}
    1 3                         {3}
    4 4                         {4, 4, 4, 4}
    2 5                         {5, 5}

If you want a hashtable for the items and their counts you just need a little ForEach-Object after it:

$array | group | % { $h = @{} } { $h[$_.Name] = $_.Count } { $h }

edited Sep 28 '12 at 14:10

answered Sep 28 '12 at 13:29

Joey

344,408
85
689
683

Thanks for this. What would be an elegant way to derive the `mode` (most frequently occurring value) of the original array? That is, given the OP's array `1 1 1 2 2 3 4 4 4 4 5 5`, I need to return `4`. – Ifedi Okonkwo Nov 04 '19 at 07:59
1

@IfediOkonkwo: `1,1,1,2,2,3,4,4,4,4,5,5 | group -NoElement | sort Count | select -last 1 -expandProperty Name`. A bit long, but each part of that pipeline does a single thing and composes well. Another option would be to separate getting the value and picking the last one with `... | group -NoElement | sort Count | % Name | select -last 1`. – Joey Nov 04 '19 at 11:15
@Joey: thanks a million. Before noticing your response, I'd cobbled something together, that worked, though more unwieldy than yours: `$hash = $Array | group | % { $h = @{} } { $h[$_.Name] = $_.Count } { $h }; $mode = $hash.GetEnumerator() | Sort-Object -Property Value -Descending | Select-Object -First 1` – Ifedi Okonkwo Nov 06 '19 at 20:11
@mklement0: I completely agree with you. But then, it's only human that laziness sometimes gets the better of you. Hopefully, google can still lead searchers to this very thread ;) – Ifedi Okonkwo Nov 06 '19 at 20:13
1

@IfediOkonkwo: Alternatively, we can [do the right thing](https://stackoverflow.com/q/58738500/45375). Note that your solution doesn't handle the case where _multiple_ values occur most frequently. – mklement0 Nov 06 '19 at 21:10
Wow! You put me to shame by that elaborate self-answered effort! Well done and +1 for both question and answer. – Ifedi Okonkwo Nov 12 '19 at 06:11

score 7 · Answer 2 · answered Sep 28 '12 at 14:08

7

You can adjust the output and format it as you like:

PS> $ht= 1,1,1,2,2,3,4,4,4,4,5,5 | Group-Object -AsHashTable -AsString
PS> $ht

Name                           Value
----                           -----
2                              {2, 2}
4                              {4, 4, 4, 4}
5                              {5, 5}
1                              {1, 1, 1}
3                              {3}


PS> $ht['1']
1
1
1

answered Sep 28 '12 at 14:08

Shay Levy

121,444
32
184
206

3

They wanted the counts, though. Thus `-AsHashTable` is of little help. – Joey Sep 28 '12 at 14:49
2

`$ht['#'].count`, in `System.Collections.Hashtable` it contains a method called `count` – Riley Carney Mar 15 '19 at 17:43

mklement0 · Answer 3 · 2019-02-27T03:56:58.407

Joey's helpful answer provides the crucial pointer: use the Group-Object cmdlet to group input objects by equality.
(To group them by one ore more of their property values instead, use -Property).

Group-Object outputs [Microsoft.PowerShell.Commands.GroupInfo] objects that each represent a group of equal input objects, whose notable properties are:

.Values ... the value(s) that define the group, as a [System.Collections.ArrayList] instance (which has just 1 element in the case at hand, since the input objects as a whole are used to form the groups).
.Count ... the count of objects in that group.

If, as in this case, there is no need to collect the individual group members as part of each group,
-NoElement can be used for efficiency.

You're free to further process the group objects as needed; to get the specific output format stipulated in your question, you can use Select-Object with a calculated property.

To put it all together:

PS> 1, 1, 1, 2, 2, 3, 4, 4, 4, 4, 5, 5 | Group-Object -NoElement |
      Select-Object @{ n='Element:Count'; e={ '{0}:{1}' -f $_.Values[0], $_.Count } }

Element:Count
-------------
1:3
2:2
3:1
4:4
5:2

Using Powershell, how can i count the occurrence of each element in an array?

3 Answers3

Linked