Supercharge Your Excel with the Double-VLOOKUP Trick

If you’re a frequent Excel user, you’re likely familiar with the VLOOKUP function - a powerful tool for linking data across multiple tables.

However, when working with large Excel files containing hundreds of thousands of rows, the VLOOKUP function can become painfully slow, sometimes taking up to an hour to recalculate your spreadsheet, often failing midway through the process. But don’t despair! There’s a technique called the Double-VLOOKUP trick that can dramatically speed up your calculations.

If you’re new to VLOOKUP, you can learn this essential function from this tutorial.

The all-too-familiar experience of waiting for Excel to calculate formulas

Understanding the Regular VLOOKUP Function

Before we dive into the Double-VLOOKUP trick, let’s quickly review how the standard VLOOKUP function works.

The VLOOKUP function is structured as follows:

VLOOKUP(lookup_value, table_array, col_index_num, [range_lookup])

Where:

• lookup_value: The ID you’re using to link your two tables. For example, if you want to look up a value for ID “1234” in another table, your lookup_value would be “1234”.
• table_array: The table in which you’re looking for the data. This table should have the IDs in the first column.
• col_index_num: The index of the column in the table_array that contains the target value you want to retrieve.
• range_lookup: The match type. This argument is crucial for our discussion. It can be TRUE or FALSE (or 1 and 0, respectively). TRUE stands for approximate match, while FALSE stands for exact match.

Here’s an example of a regular VLOOKUP function:

Example of a regular VLOOKUP function in Excel

In this example, the VLOOKUP function will return the value from column 2 when it finds the ID “1234” in the table, which is 17.

Unsorted Search Versus Binary Search

The [range_lookup] argument determines whether Excel uses an unsorted search (FALSE) or a binary search (TRUE). Here’s why this matters:

1. Unsorted Search (FALSE):

   • Excel checks each row in the table sequentially until it finds a match.
   • On average, it searches half the rows to find a match.
   • For large datasets, this can be extremely slow. For instance, with 100k rows in the first table and 200k in the second, you’re looking at potentially 10 billion operations!

2. Binary Search (TRUE):

   • Works only on sorted data.
   • Much more efficient: Excel starts by checking the middle value, then eliminates half the remaining data with each subsequent check.
   • Significantly faster than unsorted search, especially for large datasets.

Visualization of how binary search quickly narrows down the search area

The catch with binary search is that if your exact ID doesn’t exist in the table, VLOOKUP will return the closest match, which may not be what you want. This is where the Double-VLOOKUP trick comes in handy.

The Double-VLOOKUP Trick

The Double-VLOOKUP trick allows you to harness the speed of binary search while ensuring you get an exact match. Here’s how it works:

excel =IF(VLOOKUP(ID, Table, 1, TRUE)=ID, VLOOKUP(ID, Table, 2, TRUE), NA())

This formula does two things:

1. The first VLOOKUP checks if the ID exists in the table.
2. Only if the ID exists, the second VLOOKUP returns the corresponding value.

This approach prevents getting incorrect values when there’s no exact match for the ID.

Performance Improvement

The speed improvement with the Double-VLOOKUP trick is substantial:

• For a table with 10,000 rows, it’s about 28 times faster than the regular VLOOKUP.
• For a table with 1,000,000 rows, it’s up to 3,606 times faster!

These figures come from experiments conducted by Dailydoseofexcel.com.

Conclusion

While the regular VLOOKUP function is simpler for everyday use, the Double-VLOOKUP trick can be a lifesaver when dealing with large datasets that slow down your spreadsheet calculations. Remember these key points:

1. Sort your IDs before using this technique.
2. Use the Double-VLOOKUP trick when performance becomes an issue.
3. For newer versions of Excel, consider using the XLOOKUP function, which offers more flexibility and better performance than VLOOKUP.

By mastering techniques like the Double-VLOOKUP trick, you can significantly enhance your Excel productivity and handle even the largest datasets with ease.