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How to Merge Excel Files with Precision

Merging multiple Excel files into one single file can be very useful for managing and analyzing large datasets. However, care must be taken to ensure the merged data is accurate and consistent. Here are some best practices for precisely merging Excel files:

Prepare the Data in Each File

Before merging, thoroughly check the data in each file:

  • Remove duplicates – Eliminate any duplicate records to avoid skewed analysis. Use Excel’s Remove Duplicates tool.
  • Ensure consistent formatting – Date, currency, percentage formats should be consistent across files. Standardize if needed.
  • Check for errors – Scan for #REF errors indicating deleted cells, #VALUE errors from invalid data, etc. Fix all errors.
  • Add unique ID column – Add a column with a unique ID in each row to easily spot duplicate rows post-merge.

Choose the Right Merge Method

There are a few ways to combine data from multiple Excel files:

  • Copy-paste – Easy but laborious for large files. Also easy to miss rows when pasting.
  • Consolidate tool – Works by matching column headers. Limited flexibility.
  • Power Query – Automates merging of files with inconsistent formatting.
  • VBA macros – Merge via code for complex requirements. Needs VBA skills.

Power Query would be the best method for most due to its flexibility.

Merge Files in Power Query

Follow these steps:

  1. Go to Data > Get Data > From File > From Folder
  2. Select folder containing files
  3. In window that appears, select the files
  4. Click Combine & Transform
  5. Make any transformations for consistency
  6. Click Close & Load

The merged table is inserted into the worksheet.

Check for Errors Post-Merge

Scan the merged data for any anomalies introduced during merging:

  • Missing records
  • Duplicate records
  • Inconsistent formatting
  • #REF!, #VALUE! errors
  • Validation failures
  • Blank rows/cells

Look especially for above issues around rows that contain data unique to each file, like IDs.

Refresh and Update

To merge updated versions of files later:

  • Power Query – Just click Refresh to merge latest data
  • Other methods – Need to redo entire merge process

So Power Query has an advantage here as well.

Case Study

Here’s an example of precisely merging 3 Excel files, each containing a table of sales data for the years 2019, 2020 and 2021:

Sales Data Files

Preparation:

  • Removed duplicate rows in each file
  • Added unique ID column in each
  • Standardized date and currency formats

Merging:

  • Combined files using Power Query > From Folder
  • Applied Filter to only extract Sales table from each file
  • Loaded to worksheet

Post-Merge Checks:

  • Row count matches sum of rows across files
  • Randomly checked IDs are unique
  • Date and currency formats consistent
  • No errors exist

The merged table can now be easily analyzed using PivotTables, formulas, etc. And it can be refreshed whenever the source files get updated with new data.

Key Takeaways

  • Prepare files before merge by cleaning data and standardizing formats
  • Power Query offers most flexibility and automation
  • Check merged data thoroughly to catch any errors
  • Refreshable merge with Power Query avoids rebuilding from scratch

Using above best practices helps avoid common pitfalls and ensures accurately merged Excel data. This saves significant time and effort over manual merging methods while retaining precision.

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