powershell comparing multiple arrays

Question

I've a case where multiple arrays need to be compared.There is one master array that contains all the elements that the child arrays have and also some extra elements.

In below example, $a is the master array and $b, $c are child arrays. I need to compare these arrays and get the list of those extra elements in $a that are not present in $b and $c. Practically, in my case there are 10 child arrays and a master array.

$a="dhaw","roh","kohl","faf","abd","steyn","gupt","baz","kane","benn","brendn","joyc"
$b="roh","dhaw","kohl"
$c="steyn","abd","faf","roh","dhaw"

i know about the compare-object but that seems to work only for 2 arrays.i read that regex could be helpful in this case but have very little idea of how that works. — Kumar
– Kumar, Commented Mar 25, 2015 at 15:29
You need to look at using the -contains or -notcontains operator for the subject array and an array element you want to test — arco444
– arco444, Commented Mar 25, 2015 at 15:32
Compare-Objects seems to support an array of -DifferenceObjects. — Etan Reisner
– Etan Reisner, Commented Mar 25, 2015 at 15:46

Naigel · Accepted Answer · 2015-03-25 15:51:45Z

4

A viable solution could be using -notcontains operator as suggested by arco444, cycle through $a array elements and check if they are contained at least in one of the other arrays.

Here is a slice of code

foreach($a_value in $a) {
    if (($b -notcontains $a_value) -and ($c -notcontains $a_value)) {
        "$a_value is extra"
    }
}

answered Mar 25, 2015 at 15:51

Naigel

9,76417 gold badges73 silver badges111 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

beatcracker · Accepted Answer · 2015-03-25 16:03:56Z

1

Something like this?

Compare-Object -ReferenceObject $a -DifferenceObject ($b + $c)

If you just want to get raw objects:

(Compare-Object -ReferenceObject $a -DifferenceObject ($b + $c) |
    Where-Object {$_.SideIndicator -eq '<='}).InputObject

answered Mar 25, 2015 at 16:03

beatcracker

6,9601 gold badge22 silver badges44 bronze badges

Comments

mjolinor · Accepted Answer · 2015-03-25 16:27:06Z

A regex solution:

$a="dhaw","roh","kohl","faf","abd","steyn","gupt","baz","kane","benn","brendn","joyc"
$b="roh","dhaw","kohl"
$c="steyn","abd","faf","roh","dhaw"

$b_regex = ‘(?i)^(‘ + (($b |foreach {[regex]::escape($_)}) –join “|”) + ‘)$’
$c_regex = ‘(?i)^(‘ + (($c |foreach {[regex]::escape($_)}) –join “|”) + ‘)$’

Then, for elements of $a that aren't in $b:

$a -notmatch $b_regex 

faf
abd
steyn
gupt
baz
kane
benn
brendn
joyc

For elements of $a that aren't in $c:

$a -notmatch $c_regex

kohl
gupt
baz
kane
benn
brendn
joyc

And for elements of $a that aren't in $b or $c:

$a -notmatch $b_regex -notmatch $c_regex

gupt
baz
kane
benn
brendn
joyc

Runtime Regex

Note: this is just provided for demonstration for the people who left comments about it. This substantially faster than the -contains / -notcontains solutions, but for a single instance comparison it's probably overkill. It can produce substantial performance gains inside a loop where you're comparing one array to many other arrays.

Collectives™ on Stack Overflow

powershell comparing multiple arrays

3 Answers 3

Comments

Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Linked

Related