Comparing two arrays get the values which are not common

Question

i wanted a small logic to compare contents of two arrays  amp  get the value which is not common amongst them using powershell  example if   a1   1 2 3 4 5   b1   1 2 3 4 5 6     c which is the output should give me the value  6  which is the output of what s the uncommon value between both the arrays   Can some one help me out with the same  thanks

User · Accepted Answer

PS  gt   c   Compare-Object -ReferenceObject  1  5  -DifferenceObject  1  6  -PassThru PS  gt   c 6

User · Answer

This should help  uses simple hash table    a1   1 2 3 4 5   b1   1 2 3 4 5 6     hash        storing elements of  a1 in hash foreach   i in  a1    hash Add  i   present      define blank array  c  c         adding uncommon ones in second array to  c and removing common ones from hash foreach  j in  b1    if   hash ContainsKey  j    c    c  j  else  hash Remove  j       now hash is left with uncommon ones in first array  so add them to  c foreach  k in  hash keys     c    c    k

User · Answer

a   1  5  b   4  8   Yellow    a   Where   b -NotContains      Yellow contains all the items in  a except the ones that are in  b  PS C   gt   Yellow 1 2 3   Blue    b   Where   a -NotContains      Blue contains all the items in  b except the ones that are in  a  PS C   gt   Blue 6 7 8   Green    a   Where   b -Contains     Not in question  but anyways  Green contains the items that are in both  a and  b  PS C   gt   Green 4 5  Note  Where is an alias of Where-Object  Alias can introduce possible problems and make scripts hard to maintain   Addendum 12 October 2019 As commented by  xtreampb and  mklement0  although not shown from the example in the question  the task that the question implies  values  quot not in common quot   is the symmetric difference between the two input sets  the union of yellow and blue   Union The symmetric difference between the  a and  b can be literally defined as the union of  Yellow and  Blue   NotGreen    Yellow    Blue Which is written out   NotGreen     a   Where   b -NotContains          b   Where   a -NotContains       Performance As you might notice  there are quite some  redundant  loops in this syntax  all items in list  a iterate  using Where  through items in list  b  using -NotContains  and visa versa  Unfortunately the redundancy is difficult to avoid as it is difficult to predict the result of each side  A Hash Table is usually a good solution to improve the performance of redundant loops  For this  I like to redefine the question  Get the values that appear once in the sum of the collections   a    b    Count        a    b   ForEach-Object   Count        1   Count Keys   Where-Object   Count     -eq 1   By using the ForEach statement instead of the ForEach-Object cmdlet and the Where method instead of the Where-Object you might increase the performance by a factor 2 5   Count       ForEach   Item in  a    b    Count  Item     1   Count Keys Where   Count     -eq 1    LINQ But Language Integrated Query  LINQ  will easily beat any native PowerShell and native  Net methods  see also High Performance PowerShell with LINQ and mklement0 s answer for Can the following Nested foreach loop be simplified in PowerShell   To use LINQ you need to explicitly define the array types   Int    a   1  5  Int    b   4  8  And use the  Linq Enumerable    operator   Yellow      Int    Linq Enumerable   Except  a   b   Blue        Int    Linq Enumerable   Except  b   a   Green       Int    Linq Enumerable   Intersect  a   b   NotGreen    Int     Linq Enumerable   Except  a   b     Linq Enumerable   Except  b   a    Benchmark Benchmark results highly depend on the sizes of the collections and how many items there are actually shared  as a  quot average quot   I am presuming that half of each collection is shared with the other  Using             Time Compare-Object    111 9712 NotContains       197 3792 ForEach-Object    82 8324 ForEach Statement 36 5721 LINQ              22 7091  To get a good performance comparison  caches should be cleared by e g  starting a fresh PowerShell session   a   1  1000  b   500  1500   Measure-Command       Compare-Object -ReferenceObject  a -DifferenceObject  b  -PassThru    TotalMilliseconds  Measure-Command         a   Where   b -NotContains         b   Where   a -NotContains         TotalMilliseconds  Measure-Command        Count            a    b   ForEach-Object   Count        1       Count Keys   Where-Object   Count     -eq 1     TotalMilliseconds   Measure-Command        Count           ForEach   Item in  a    b    Count  Item     1       Count Keys Where   Count     -eq 1      TotalMilliseconds   Int    a    a  Int    b    b  Measure-Command        Int     Linq Enumerable   Except  a   b     Linq Enumerable   Except  b   a      TotalMilliseconds

User · Answer

Your results will not be helpful unless the arrays are first sorted   To sort an array  run it through Sort-Object     x     5 1 4 2 3   y     2 4 6 1 3 5   Compare-Object -ReferenceObject   x   Sort-Object  -DifferenceObject   y   Sort-Object

User · Answer

Try    a1   1 2 3 4 5   b1   1 2 3 4 5 6   Compare-Object  a1  b1  InputObject   Or  you can use    Compare-Object  b1  a1  InputObject   The order doesn t matter

User · Answer

Look at Compare-Object  Compare-Object  a1  b1   ForEach-Object      InputObject     Or if you would like to know where the object belongs to  then look at SideIndicator    a1   1 2 3 4 5 8   b1   1 2 3 4 5 6  Compare-Object  a1  b1

[arrays] Comparing two arrays & get the values which are not common

Examples related to arrays

Examples related to powershell