Removing Outliers with the Array Formula


The ARRAYFORMULA function is very useful and differs from the ones you might be using day in / day out such as SUM. It allows the use of a formula with arrays which basically means it will apply some logic to every single cell within a range and return a range of values or array. A simple formula like SUM or AVERAGE returns one value only. Let’s go through one example.

Quick look at the data:

Let’s say we have the number of daily website visitors for a specific period of time, and we want to easily remove the outliers: values that deviate significantly from the observations. To keep it simple we will define outliers as values beyond the mean + 2 times the standard deviation. Here is the dataset:


Let’s apply the formula:

If we type the following formula in cell C2:

=ARRAYFORMULA(if(B2:B10 > average(B2:B10) + 2 * STDEV.S(B2:B10), "", B2:B10))

we then managed to identify and remove one outlier:


Et voila!

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