There are two recurring problems that Random People who Care face in Excel:

• From a set of data, get a list of the unique items in the data. There might be a table with a "site" column, and Random People who Care need to get a list of the sites.
• Perform an operation on an array of values selected based on these unique data. There might be interest, for example, in calculating the average measurement for each site.

Unique Items from a List

Let's start with a simplified table representing data about measurements taken at some sites.

To get a list of unique sites, we use the Data -> filter -> "advanced filter" to copy the unique values from the site column to a new blank set of cells.

Calculation selected by Unique Item

Now for each site, we want the mean "bing". This could be micrograms of mercury per gallon of water, or whatever. To do that, use an array formula, as described elsewhere [click here].

In the picture below, I'm about to type two closing parentheses and then the magic keys: control+shift+enter. I can't just type in the parens and hit enter. Without control+shift+enter, the array formula won't work!