PowerShell script to group records by overlapping start and end date - powershell

Question

I am working on a CSV file which have start and end date and the requirement is group records by dates when the dates overlap each other.
For example, in below table Bill_Number 177835 Start_Date and End_Date is overlapping with 178682,179504, 178990 Start_Date and End_Date so all should be grouped together and so on for each and every record.
Bill_Number,Start_Date,End_Date
177835,4/14/20 3:00 AM,4/14/20 7:00 AM
178682,4/14/20 3:00 AM,4/14/20 7:00 AM
179504,4/14/20 3:29 AM,4/14/20 6:29 AM
178662,4/14/20 4:30 AM,4/14/20 5:30 AM
178990,4/14/20 6:00 AM,4/14/20 10:00 AM
178995,4/15/20 6:00 AM,4/15/20 10:00 AM
178998,4/15/20 6:00 AM,4/15/20 10:00 AM
I have tried different combination like "Group-by" and "for loop" but not able to produce result.
With the above example of CSV, the expected result is;
Group1: 177835,178682,179504, 178990
Group2: 177835,178682,179504, 178662
Group3: 178995, 178998
Currently i have below code in hand.
Any help on this will be appreciated,thanks in advance.
$array = #(‘ab’,’bc’,’cd’,’df’)
for ($y = 0; $y -lt $array.count) {
for ($x = 0; $x -lt $array.count) {
if ($array[$y]-ne $array[$x]){
Write-Host $array[$y],$array[$x]
}
$x++
}
$y++
}

Answer 1

You can do something like the following. There is likely a cleaner solution, but that could take a lot of time.
$csv = Import-Csv file.csv
# Creates all inclusive groups where times overlap
$csvGroups = foreach ($row in $csv) {
$start = [datetime]$row.Start_Date
$end = [datetime]$row.End_Date
,($csv | where { ($start -ge [datetime]$_.Start_Date -and $start -le [datetime]$_.End_Date) -or ($end -ge [datetime]$_.Start_Date -and $end -le [datetime]$_.End_Date) })
}
# Removes duplicates from $csvGroups
$groups = $csvGroups | Group {$_.Bill_number -join ','} |
Foreach-Object { ,$_.Group[0] }
# Compares current group against all groups except itself
$output = for ($i = 0; $i -lt $groups.count; $i++) {
$unique = $true # indicates if the group's bill_numbers are in another group
$group = $groups[$i]
$list = $groups -as [system.collections.arraylist]
$list.RemoveAt($i) # Removes self
foreach ($innerGroup in $list) {
# If current group's bill_numbers are in another group, skip to next group
if ((compare $group.Bill_Number $innergroup.Bill_Number).SideIndicator -notcontains '<=') {
$unique = $false
break
}
}
if ($unique) {
,$group
}
}
$groupCounter = 1
# Output formatting
$output | Foreach-Object { "Group{0}:{1}" -f $groupCounter++,($_.Bill_Number -join ",")}
Explanation:
I added comments to give an idea as to what is going on.
The ,$variable syntax uses the unary operator ,. It converts the output into an array. Typically, PowerShell unrolls an array as individual items. The unrolling becomes a problem here because we want the groups to stays as groups (arrays). Otherwise, there would be a lot of duplicate bill numbers, and we'd lose track between groups.
An arraylist is used for $list. This is so we can access the RemoveAt() method. A typical array is of fixed size and can't be manipulated in that fashion. This can effectively be done with an array, but the code is different. You either have to select the index ranges around the item you want to skip or create a new array using some other conditional statement that will exclude the target item. An arraylist is just easier for me (personal preference).

Answer 2

So a very dirty approach. I think there are a coup of ways to determine if there's overlap for a specific comparison, one record to another. However you may need a list of bill numbers each bill date range collides with. using a function call in a Select-Object statement/expression I added a collisions property to your objects.
The function is wordy and probably be improved, but the gist is that for each record it will compare to all other records and report that bill number in it's collision property if either the start or end date falls within the other records range.
This is of course just demo code, I'm sure it can be made better for your purposes, but may be a starting point for you.
Obviously change the path to the CSV file.
Function Get-Collisions
{
Param(
[Parameter(Mandatory = $true)]
[Object]$ReferenceObject,
[Parameter( Mandatory = $true )]
[Object[]]$CompareObjects
) # End Parameter Block
ForEach($Object in $CompareObjects)
{
If( !($ReferenceObject.Bill_Number -eq $Object.Bill_Number) )
{
If(
( $ReferenceObject.Start_Date -ge $Objact.StartDate -and $ReferenceObject.Start_Date -le $Objact.End_Date ) -or
( $ReferenceObject.End_Date -ge $Object.Start_Date -and $ReferenceObject.End_Date -le $Object.End_Date ) -or
( $ReferenceObject.Start_Date -le $Object.Start_Date -and $ReferenceObject.End_Date -ge $Object.Start_Date )
)
{
$Object.Bill_Number
}
}
}
} # End Get-Collisions
$Objects = Import-Csv 'C:\temp\DateOverlap.CSV'
$Objects |
ForEach-Object{
$_.Start_Date = [DateTime]$_.Start_Date
$_.End_Date = [DateTime]$_.End_Date
}
$Objects = $Objects |
Select-object *,#{Name = 'Collisions'; Expression = { Get-Collisions -ReferenceObject $_ -CompareObjects $Objects }}
$Objects | Format-Table -AutoSize
Let me know how it goes. Thanks.

Answer 3

#Shan , I saw your comments so I wanted to respond with some additional code and discussion. I may have gone overboard, but you expressed a desire to learn, such that you can maintain these code pieces in the future. So, I put a lot of time into this.
I may mention some of #AdminOfThings work too. That is not criticism, but collaboration. His example is clever and dynamic in terms of getting the job done and pulling in the right tools as he worked his way to the desired output.
I originally side-stepped the grouping question because I didn't feel like naming/numbering the groups had any meaning. For example: "Group 1" indicates all its members have overlap in their billing periods, but no indication of what or when the overlap is. Maybe I rushed through it… I may have been reading too much into it or perhaps even letting my own biases get in the way. At any rate, I elected to create a relationship from the perspective of each bill number, and that resulted in my first answer.
Since then, and because of your comment, I put effort into extending and documenting the first example I gave. The revised code will be Example 1 below. I've heavily commented it and most of the comments will apply to the original example as well. There are some differences that were forced by the extended grouping functionality, but the comments should reflect those situations.
Note: You'll also see I stopped calling them "collisions" and termed them "overlaps" instead.
Example 1:
Function Get-Overlaps
{
<#
.SYNOPSIS
Given an object (reference object) compare to a collection of other objects of the same
type. Return an array of billing numbers for which the billing period overlaps that of
the reference object.
.DESCRIPTION
Given an object (reference object) compare to a collection of other objects of the same
type. Return an array of billing numbers for which the billing period overlaps that of
the reference object.
.PARAMETER ReferenceObject
This is the current object you wish to compare to all other objects.
.PARAMETER
The collection of objects you want to compare with the reference object.
.NOTES
> The date time casting could probably have been done by further preparing
the objects in the calling code. However, givin this is for a
StackOverflow question I can polish that later.
#>
Param(
[Parameter(Mandatory = $true)]
[Object]$ReferenceObject,
[Parameter( Mandatory = $true )]
[Object[]]$CompareObjects
) # End Parameter Block
[Collections.ArrayList]$Return = #()
$R_StartDate = [DateTime]$ReferenceObject.Start_Date
$R_EndDate = [DateTime]$ReferenceObject.End_Date
ForEach($Object in $CompareObjects)
{
$O_StartDate = [DateTime]$Object.Start_Date
$O_EndDate = [DateTime]$Object.End_Date
# The first if statement skips the reference object's bill_number
If( !($ReferenceObject.Bill_Number -eq $Object.Bill_Number) )
{
# This logic can use some explaining. So far as I could tell there were 2 cases to look for:
# 1) Either or both the start and end dates fell inside the the timespan of the comparison
# object. This cases is handle by the first 2 conditions.
# 2) If the reference objects timespan covers the entire timespan of the comparison object.
# Meaning the start date is before and the end date is after, fitting the entire
# comparison timespan is within the bounds of the reference timespan. I elected to use
# the 3rd condition below to detect that case because once the start date is earlier I
# only have to care if the end date is greater than the start date. It's a little more
# inclusive and partially covered by the previous conditions, but whatever, you gotta
# pick something...
#
# Note: This was a deceptively difficult thing to comprehend, I missed that last condition
# in my first example (later corrected) and I think #AdminOfThings also overlooked it.
If(
( $R_StartDate -ge $O_StartDate -and $R_StartDate -le $O_EndDate ) -or
( $R_EndDate -ge $O_StartDate -and $R_EndDate -le $O_EndDate ) -or
( $R_StartDate -le $O_StartDate -and $R_EndDate -ge $O_StartDate )
)
{
[Void]$Return.Add( $Object.Bill_Number )
}
}
}
Return $Return
} # End Get-Overlaps
$Objects =
Import-Csv 'C:\temp\DateOverlap.CSV' |
ForEach-Object{
# Consider overlap as a relationship from the perspective of a given Object.
$Overlaps = [Collections.ArrayList]#(Get-overlaps -ReferenceObject $_ -CompareObjects $Objects)
# Knowing the overlaps I can infer the group, by adding the group's bill_number to its group property.
If( $Overlaps )
{ # Don't calculate a group unless you actually have overlaps:
$Group = $Overlaps.Clone()
[Void]$Group.Add( $_.Bill_Number ) # Can you do in the above line, but for readability I separated it.
}
Else { $Group = $null } # Ensure's not reusing group from a previous iteration of the loop.
# Create a new PSCustomObject with the data so far.
[PSCustomObject][Ordered]#{
Bill_Number = $_.Bill_Number
Start_Date = [DateTime]$_.Start_Date
End_Date = [DateTime]$_.End_Date
Overlaps = $Overlaps
Group = $Group | Sort-Object # Sorting will make it a lot easier to get unique lists later.
}
}
# The reason I recreated the objects from the CSV file instead of using Select-Object as I had
# previously is that I simply couldn't get Select-Object to maintain type ArrayList that was being
# returned from the function. I know that's a documented problem or circumstance some where.
# Now I'll add one more property called Group_ID a comma delimited string that we can later use
# to echo the groups according to your original request.
$Objects =
$Objects |
Select-Object *,#{Name = 'Group_ID'; Expression = { $_.Group -join ', ' } }
# This output is just for the sake of showing the new objects:
$Objects | Format-Table -AutoSize -Wrap
# Now create an array of unique Group_ID strings, this is possible of the sorts and joins done earlier.
$UniqueGroups = $Objects.Group_ID | Select-Object -Unique
$Num = 1
ForEach($UniqueGroup in $UniqueGroups)
{
"Group $Num : $UniqueGroup"
++$Num # Increment the $Num, using convienient unary operator, so next group is echoed properly.
}
# Below is a traditional for loop that does the same thing. I did that first before deciding the ForEach
# was cleaner. Leaving it commented below, because you're on a learning-quest, so just more demo code...
# For($i = 0; $i -lt $UniqueGroups.Count; ++$i)
# {
# $Num = $i + 1
# $UniqueGroup = $UniqueGroups[$i]
# "Group $Num : $UniqueGroup"
# }
Example 2:
$Objects =
Import-Csv 'C:\temp\DateOverlap.CSV' |
Select-Object Bill_Number,
#{ Name = 'Start_Date'; Expression = { [DateTime]$_.Start_Date } },
#{ Name = 'End_Date'; Expression = { [DateTime]$_.End_Date } }
# The above select statement converts the Start_Date & End_Date properties to [DateTime] objects
# While you had asked to pack everything into the nested loops, that would have resulted in
# unnecessary recasting of object types to ensure proper comparison. Often this is a matter of
# preference, but in this case I think it's better. I did have it working well without the
# above select, but the code is more readable / concise with it. So even if you treat the
# Select-Object command as a blackbox the rest of the code should be easier to understand.
#
# Of course, and if you couldn't tell from my samples Select-Object is incredibly useful. I
# recommend taking the time to learn it thoroughly. The MS documentation can be found here:
# https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/select-object?view=powershell-5.1
:Outer ForEach( $ReferenceObject in $Objects )
{
# In other revisions I had assigned these values to some shorter variable names.
# I took that out. Again since you're learning I wanted the all the dot referencing
# to be on full display.
$ReferenceObject.Start_Date = $ReferenceObject.Start_Date
$ReferenceObject.End_Date = $ReferenceObject.End_Date
[Collections.ArrayList]$TempArrList = #() # Reset this on each iteration of the outer loop.
:Inner ForEach( $ComparisonObject in $Objects )
{
If( $ComparisonObject.Bill_Number -eq $ReferenceObject.Bill_Number )
{ # Skip the current reference object in the $Objects collection! This prevents the duplication of
# the current Bill's number within it's group, helping to ensure unique-ification.
#
# By now you should have seen across all revision including AdminOfThings demo, that there was some
# need skip the current item when searching for overlaps. And, that there are a number of ways to
# accomplish that. In this case I simply go back to the top of the loop when the current record
# is encountered, effectively skipping it.
Continue Inner
}
# The below logic needs some explaining. So far as I could tell there were 2 cases to look for:
# 1) Either or both the start and end dates fell inside the the timespan of the comparison
# object. This cases is handle by the first 2 conditions.
# 2) If the reference object's timespan covers the entire timespan of the comparison object.
# Meaning the start date is before and the end date is after, fitting the entire
# comparison timespan is within the bounds of the reference timespan. I elected to use
# the 3rd condition below to detect that case because once the start date is earlier I
# only have to care if the end date is greater than the other start date. It's a little
# more inclusive and partially covered by the previous conditions, but whatever, you gotta
# pick something...
#
# Note: This was a deceptively difficult thing to comprehend, I missed that last condition
# in my first example (later corrected) and I think #AdminOfThings also overlooked it.
If(
( $ReferenceObject.Start_Date -ge $ComparisonObject.Start_Date -and $ReferenceObject.Start_Date -le $ComparisonObject.End_Date ) -or
( $ReferenceObject.End_Date -ge $ComparisonObject.Start_Date -and $ReferenceObject.End_Date -le $ComparisonObject.End_Date ) -or
( $ReferenceObject.Start_Date -le $ComparisonObject.Start_Date -and $ReferenceObject.End_Date -ge $ComparisonObject.Start_Date )
)
{
[Void]$TempArrList.Add( $ComparisonObject.Bill_Number )
}
}
# Now Add the properties!
$ReferenceObject | Add-Member -Name Overlaps -MemberType NoteProperty -Value $TempArrList
If( $ReferenceObject.Overlaps )
{
[Void]$TempArrList.Add($ReferenceObject.Bill_Number)
$ReferenceObject | Add-Member -Name Group -MemberType NoteProperty -Value ( $TempArrList | Sort-Object )
$ReferenceObject | Add-Member -Name Group_ID -MemberType NoteProperty -Value ( $ReferenceObject.Group -join ', ' )
# Below a script property also works, but I think the above is easier to follow:
# $ReferenceObject | Add-Member -Name Group_ID -MemberType ScriptProperty -Value { $this.Group -join ', ' }
}
Else
{
$ReferenceObject | Add-Member -Name Group -MemberType NoteProperty -Value $null
$ReferenceObject | Add-Member -Name Group_ID -MemberType NoteProperty -Value $null
}
}
# This output is just for the sake of showing the new objects:
$Objects | Format-Table -AutoSize -Wrap
# Now create an array of unique Group_ID strings, this is possible of the sorts and joins done earlier.
#
# It's important to point out I chose to sort because I saw the clever solution that AdminOfThings
# used. There's a need to display only groups that have unique memberships, not necessarily unique
# ordering of the members. He identified these by doing some additional loops and using the Compare
# -Object cmdlet. Again, I must say that was very clever, and Compare-Object is another tool very much
# worth getting to know. However, the code didn't seem like it cared which of the various orderings it
# ultimately output. Therefore I could conclude the order wasn't really important, and it's fine if the
# groups are sorted. With the objects sorted it's much easier to derive the truely unique lists with the
# simple Select-Object command below.
$UniqueGroups = $Objects.Group_ID | Select-Object -Unique
# Finally Loop through the UniqueGroups
$Num = 1
ForEach($UniqueGroup in $UniqueGroups)
{
"Group $Num : $UniqueGroup"
++$Num # Increment the $Num, using convienient unary operator, so next group is echoed properly.
}
Additional Discussion:
Hopefully the examples are helpful. I wanted to mentioned a few more points:
Using ArrayLists ( [System.Collections.ArrayList] ) instead of native arrays. The typical reason to do this is the ability to add and remove elements quickly. If you search the internet you'll find hundreds of articles explaining why it's faster. It's so common you'll often find experienced PowerShell users implementing it instinctively. But the main reason is speed and the flexibility to easily add and remove elements.
You'll notice I relied heavily on the ability to append new properties to objects. There are several ways to do this, Select-Object , Creating your own objects, and in Example 2 above I used Get-Member. The main reason I used Get-Member was I couldn't get the ArrayList type to stick when using Select-Object.
Regarding loops. This is specific to your desire for nested loops. My first answer still had loops, except some were implied by the pipe, and others were stored in a helper function. The latter is really also a preference; for readability it's sometimes helpful to park some code out of view from the main code body. That said, all the same concepts were there from the beginning. You should get comfortable with the implied loop that comes with pipe-lining capability.
I don't think there's much more I can say without getting redundant. I really hope this was helpful, it was certainly fun for me to work on it. If you have questions or feedback let me know. Thanks.