How to merge multiple CSV files

After buying several SmartPacks you may want one combined file.

Before merging

1. Check the headers match. Packs from the same dataset version share a column layout. Packs from different versions may not — compare the first line of each file.
2. Use one encoding. Our files are UTF-8. Mixing in files saved as Windows-1252 from other sources will corrupt accented characters.

Windows (PowerShell)

$files = Get-ChildItem .\UK-*.csv | Sort-Object Name
Get-Content $files[0] -TotalCount 1 | Set-Content merged.csv -Encoding utf8
foreach ($f in $files) { Get-Content $f | Select-Object -Skip 1 | Add-Content merged.csv -Encoding utf8 }

macOS / Linux

head -n 1 UK-0001.csv > merged.csv
for f in UK-*.csv; do tail -n +2 "$f" >> merged.csv; done

Python (pandas)

import glob, pandas as pd
frames = [pd.read_csv(f, dtype=str) for f in sorted(glob.glob("UK-*.csv"))]
pd.concat(frames, ignore_index=True).to_csv("merged.csv", index=False)

dtype=str keeps phone numbers and postcodes exactly as delivered.

After merging

Run a duplicate check on a normalised key (phone in E.164 or website domain) — see how duplicates are measured. Then count the rows to confirm nothing was lost: the merged file should contain the sum of the individual row counts minus any duplicates you removed.