Answer to reddit question https://www.reddit.com/r/PowerShell/comments/v5ey6d/powershell_command_to_move_files_to_fodlers_with/?utm_source=share&utm_medium=web2x&context=3

movecommonfiles.ps1

  function Get-StringLCP
{
<#
.SYNOPSIS
  Get the longest common string prefix from an array of strings.

.DESCRIPTION
  Get the longest common string prefix from an array of strings.
  Note that empty strings and null values are allowed in the array.
  Nulls will be automatically type cast by PowerShell as an empty string.
  Use the IgnoreEmptyStrings switch to stop processing empty strings.

.PARAMETER InputStrings
  The array of strings from which the longest common prefix is sought.

.PARAMETER IgnoreEmptyStrings
  Excludes empty strings from the processing. Use this option when the input
  data may have nulls or empty strings. If a null or empty string is present
  the return value will always be [string]::Empty

.PARAMETER IgnoreCase
  Performs case insensitive comparisons on the strings

.INPUTS
  <None>

.OUTPUTS
  [string]

.NOTES
  Version:        1.0
  Author:         Robert Thomson
  Creation Date:  2022-03-19
  Purpose/Change: Initial rewrite of code at rosettacode.org, as an advanced
    function with options for case insensitive comparison and empty string
    filtering.
  References:
    1) Longest common prefix - Rosetta Code. Rosettacode.org. (2022).
        Retrieved 19 March 2022, from
        https://rosettacode.org/wiki/Longest_common_prefix#PowerShell.

.EXAMPLE
  Get-StringLCP -InputStrings @('foo', 'foobar')

  This example performs a case-sensitive comparison to return 'foo'.

.EXAMPLE
  Get-StringLCP -InputStrings @('foo', 'FOOBAR') -IgnoreCase

  This example performs a case-insensitive comparison to return 'foo'.

.EXAMPLE
  Get-StringLCP -InputStrings @('foo', $null, 'foobar')
  Get-StringLCP -InputStrings @('foo', '', 'foobar')

  These examples are equivalent and perform a case-sensitive comparison to return ''.

.EXAMPLE
  Get-StringLCP -InputStrings @('foo', $null, 'foobar') -IgnoreEmptyStrings
  Get-StringLCP -InputStrings @('foo', '', 'foobar') -IgnoreEmptyStrings

  These examples are equivalent and perform a case-sensitive comparison to return 'foo'.

#>
    [CmdletBinding()]
    param(
        [parameter(Mandatory)]
        [AllowEmptyCollection()]
        [AllowEmptyString()]
        [string[]]$InputStrings,

        [parameter()]
        [Switch]$IgnoreEmptyStrings,

        [parameter()]
        [Switch]$IgnoreCase
    )

    if ($IgnoreEmptyStrings.IsPresent) {
        $arr = ($InputStrings | Where-Object {
            ![String]::IsNullOrEmpty($_)
        } | Sort-Object -Property {$_.length} | Select-Object -unique) -as [String[]]
    }
    else {
        $arr = ($InputStrings | Sort-Object -Property {$_.length} | Select-Object -unique) -as [String[]]
    }

    switch ($arr.count) {
        # Array is null or empty
        0 {[string]::Empty}

        # Longest common prefix of a single string is the string
        1 {$arr[0]}

        # Process 2 or more strings.
        default {
            $Limit = $arr[0].length
            $i = 0
            $test = $true

            # Configure the grouping property scriptblock for case insensitive if required
            if ($IgnoreCase.IsPresent) {
                $sb = {[char]::ToUpper($_[$i])}
            }
            else {
                $sb = {$_[$i]}
            }
            while (($i -lt $Limit) -and $test) {
                # Group by letter. If the letters are the same for all the strings there will be only one group
                $test = ($arr | Group-Object -Property $sb ).Name.Count -eq 1
                if ($test) {
                    $i++
                }
            }
            $arr[0].substring(0,$i)
        }
    }
}


# Main script part (untested)

$files = Get-ChildItem -Path .\ -File
$filenames = $files.Name
$Start = $End = 0
while ($start -lt $filenames.count -and $end -lt $filenames.count) {
    do {
        $lcp = Get-StringLCP -IgnoreCase -InputStrings $filenames[$start..$end++] 
    } while (-not [string]::IsNullOrEmpty($lcp))
    if (($end - $start) -gt 1) {
        $lcp = Get-StringLCP -IgnoreCase -InputStrings $filenames[$start..($end - 1)]
        New-Item -Path ".\$lcp" -ItemType Directory
        Move-Item -path $filenames[$start..($end - 1)] -Destination ".\$lcp"
    }
    $start = $End 
}