Powershell: How to merge unique headers from one CSV to another?

Question

Edit 1:

So I've figure out how to get the unique headers in CSV 2 to append to CSV 1.

$header = ($table | Get-Member -MemberType NoteProperty).Name
$header_add = ($table_add | Get-Member -MemberType NoteProperty).Name
$header_diff = $header + $header_add
$header_diff = ($header_diff | Sort-Object -Unique)
$header_diff = (Compare-Object -ReferenceObject $header -DifferenceObject $header_diff -PassThru)

$header is an array of headers from CSV 1 ($table). $header_add is an array of headers from CSV 2 ($table_add). $header_diff houses the unique headers in CSV 2 by the end of the code block.

So as far as I'm aware, my next step would be:

$append = ($table_add | Select-Object $header_diff)

My problem now is how do I append these objects to my CSV 1 ($table 1) object? I don't quite see a way for Add-Member to do this in a particularly nice fashion.

---

Original:

Here's the headers for the two CSV files I'm trying to combine.

CSV 1:

Date, Name, Assigned Router, City, Country, # of Calls  , Calls in  , Calls out

CSV 2:

Date, Name, Assigned Router, City, Country, # of Minutes, Minutes in, Minutes out

So a quick rundown of what these files are; both files contain call information for a set of names for one day (the date column has the same date for each row; this is because this eventually gets sent to a master .xlsx file with all dates combined). All of the columns up to Country contain the same values in the same order in both files. The files simply separate the # of calls and # of minutes data. I was wondering if there was a convenient way to move the unlike columns from one CSV to another.

I've tried using something along the lines of:

Import-Csv (Get-ChildItem <directory> -Include <common pattern in file pair>) | Export-Csv <output path> -NoTypeInformation

This didn't combine all of the matching headers and append the unique ones afterwards. Only the first file that's processed kept its unique headers. The second file that was processed had all of those headers and data discarded in the output. Shared header data in the second CSV was added as additional rows.

An example output of my described fail output:

PS > $small | Format-Table

Column_1 Column_2 Column_3
-------- -------- --------
1        a        a
1        b        b
1        c        c


PS > $small_add | Format-Table

Column_1 Column_4 Column_5
-------- -------- --------
1        x        x
1        y        y
1        z        z


PS > Import-Csv (Get-ChildItem ./*.* -Include "small*.csv") | Select-Object * -unique | Format-Table

Column_1 Column_2 Column_3
-------- -------- --------
1        a        a
1        b        b
1        c        c
1
1
1

I was wondering if I could do something like the following algorithm:

1. Import-Csv CSV_1 and CSV_2 to separate variables

2. Compare CSV_2 headers to CSV_1 headers, storing the unlike headers in CSV_2 into a separate variable

3. Select-Object all CSV_1 headers and unlike CSV_2 headers

4. Pipe the Select-Object output to Export-Csv

The only other method I could only think of is doing it line by line where I would:

1. Import-Csv both

2. remove all of the shared columns from CSV_2

3. change it from the custom object Powershell uses for CSVs to a string

4. append each line of CSV_2 to each line of CSV_1

It feels a bit unrefined and inflexible (flexibility can probably be dealt with by how columns/headers are isolated so there's no problem appending strings).

Answer 1

<sup>* This answer focuses on a high-level-of-abstraction OO solution.
* The OP's own solution relies more on string processing, which has the potential to be faster.</sup>

# The input file paths.
$files = 'csv1.csv', 'csv2.csv'
$outFile = 'csvMerged.csv'

# Read the 2 CSV files into collections of custom objects.
# Note: This reads the entire files into memory.
$doc1 = Import-Csv $files[0]
$doc2 = Import-Csv $files[1]

# Determine the column (property) names that are unique to document 2.
$doc2OnlyColNames = (
  Compare-Object $doc1[0].psobject.properties.name $doc2[0].psobject.properties.name |
    Where-Object SideIndicator -eq '=>'
).InputObject

# Initialize an ordered hashtable that will be used to temporarily store
# each document 2 row's unique values as key-value pairs, so that they
# can be appended as properties to each document-1 row.
$htUniqueRowD2Props = [ordered] @{}

# Process the corresponding rows one by one, construct a merged output object
# for each, and export the merged objects to a new CSV file.
$i = 0
$(foreach($rowD1 in $doc1) {
  # Get the corresponding row from document 2.
  $rowD2 = $doc2[$i++]
  # Extract the values from the unique document-2 columns and store them in the ordered
  # hashtable.
  foreach($pname in $doc2OnlyColNames) { $htUniqueRowD2Props.$pname = $rowD2.$pname }
  # Add the properties represented by the hashtable entries to the
  # document-1 row at hand and output the augmented object (-PassThru).
  $rowD1 | Add-Member -NotePropertyMembers $htUniqueRowD2Props -PassThru
}) | Export-Csv -NoTypeInformation -Encoding Utf8 $outFile

---

To put the above to the test, you can use the following sample input:

# Create sample input CSV files
@'
Date,Name,Assigned Router,City,Country,# of Calls,Calls in,Calls out
dt,nm,ar,ct,cy,cc,ci,co
dt2,nm2,ar2,ct2,cy2,cc2,ci2,co2
'@ > csv1.csv

# Same column layout and data as above through column 'Country', then different.
@'
Date,Name,Assigned Router,City,Country,# of Minutes,Minutes in,Minutes out
dt,nm,ar,ct,cy,mc,mi,mo
dt2,nm2,ar2,ct2,cy2,mc2,mi2,mo2
'@ > csv2.csv

The code should produce the following content in csvMerged.csv:

"Date","Name","Assigned Router","City","Country","# of Calls","Calls in","Calls out","# of Minutes","Minutes in","Minutes out"
"dt","nm","ar","ct","cy","cc","ci","co","mc","mi","mo"
"dt2","nm2","ar2","ct2","cy2","cc2","ci2","co2","mc2","mi2","mo2"

Answer 2

Edit 1:

# Read 2 CSVs into PowerShell CSV object
$table = Import-Csv test.csv
$table_add = Import-Csv test_add.csv

# Isolate unique headers in second CSV
$unique_headers = (Compare-Object -ReferenceObject $table[0].PSObject.Properties.Name -DifferenceObject $table_add[0].PSObject.Properties.Name | Where-Object SideIndicator -eq "=>").InputObject

# Convert CSVs to strings, with second CSV only containing unique columns
$table_str = ($table | ConvertTo-Csv -NoTypeInformation)
$table_add_str = ($table_add | Select-Object $unique_headers | ConvertTo-Csv -NoTypeInformation)

# Append CSV 2's unique columns to CSV 1

# Set line counter
$line = 0

# Concatenate CSV 2 lines to the end of CSV 1 lines until one or both are out of lines
While (($table_str[$line] -ne $null) -and ($table_add_str[$line] -ne $null)) {
    If ($line -eq 0) {
        $table_sum_str = $table_str[$line] + "," + $table_add_str[$line]
    }
    If ($line -ne 0) {
        $table_sum_str = $table_sum_str + "`n" + ($table_str[$line] + "," + $table_add_str[$line])
    }
    $line = $line + 1
}
$table_sum_str | Set-Content -Path $outpath -Encoding UTF8

Using Measure-Command, the above code on my machine for the most part takes anywhere between 14-17 milliseconds to run. Running Measure-Command on mklement's yields effectively the same times from just eyeballing it.

Note that for both solutions, the data in the 2 CSV files must be in the same order. If you want to add 2 CSVs together that have complimentary data but in different orders, you need to use mklement's object oriented approach and add mechanisms to match the data to a location or name.

---

Original:

For those who don't want to use a hash table to do this:

# Make sure you're in same directory as files:

# CSV 1
$table = Import-Csv test.csv
# CSV 2
$table_add = Import-Csv test_add.csv

# Get array with CSV 1 headers
$header = ($table | Get-Member -MemberType NoteProperty).Name
# Get array with CSV 2 headers
$header_add = ($table_add | Get-Member -MemberType NoteProperty).Name

# Add arrays of both headers together
$header_diff = $header + $header_add
# Sort the headers, remove duplicate headers (first couple ones), keep unique ones
$header_diff = ($header_diff | Sort-Object -Unique)
# Remove all of CSV 1's unique headers and shared headers
$header_diff = (Compare-Object -ReferenceObject $header -DifferenceObject $header_diff -PassThru)

# Generate a CSV table containing only CSV 2's unique headers
$table_diff = ($table_add | Select-Object $header_diff)

# Convert CSV 1 from a custom PSObject to a string
$table_str = ($table | Select-Object * | ConvertTo-Csv)

# Convert CSV 2 (unique headers only) from custom PSObject to a string
$table_diff_str = ($table_diff | Select-Object * | ConvertTo-Csv)

# Set line counter
$line = 0
# Set flag for if headers have been processed
$headproc = 0
# Concatenate CSV 2 lines to the end of CSV 1 lines until one or both are out of lines.
While (($table_str[$line] -ne $null) -and ($table_diff_str[$line] -ne $null)) {
  If ($headproc -eq 1) {
      $table_sum_str = $table_sum_str + "`n" + ($table_str[$line] + "," + $table_diff_str[$line])
  }
  If ($headproc -eq 0) {
      $table_sum_str = $table_str[$line] + "," + $table_diff_str[$line]
      $headproc = 1
  }
    $line = $line + 1
}
$table_sum_str | ConvertFrom-Csv | Select-Object * | Export-Csv -Path "./test_sum.csv" -Encoding UTF8 -NoTypeInformation

Ran a quick comparison using Measure-Command between this and mklement0's script.

PS > Measure-Command {./self.ps1}


Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 0
Milliseconds      : 26
Ticks             : 267771
TotalDays         : 3.09920138888889E-07
TotalHours        : 7.43808333333333E-06
TotalMinutes      : 0.000446285
TotalSeconds      : 0.0267771
TotalMilliseconds : 26.7771


PS > Measure-Command {./mklement.ps1}


Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 0
Milliseconds      : 18
Ticks             : 185058
TotalDays         : 2.141875E-07
TotalHours        : 5.1405E-06
TotalMinutes      : 0.00030843
TotalSeconds      : 0.0185058
TotalMilliseconds : 18.5058

I assume speed differences are because I spend time creating a separate CSV PSObject to isolate columns instead of comparing them directly. mklement's also has the advantage of keeping the columns in the same order.