What Are Measures Collections for?

Briefly

Measures collections automatically record information from their source collections.

It's best to explain this with an example.

Suppose you have a collection, coins, that represents 10 coins. Each case has one attribute, face, which is randomly heads or tails. You can flip the coins again by pressing control-Y. Sometimes you get three heads, sometimes six, and so forth. You decide to record how many heads come up whenever you flip those ten coins.

You could do it by hand just make a new collection and record the numbers but Fathom can do it for you automatically if you use a measures collection.

You have to tell Fathom what you want to record. You do that by making a measure in your coins collection. Call it N_Heads and give it a formula like count( face = "heads" ). Now make your measures collection. When you collect many measures, it will contain the results from as many tossings of the ten coins as you like.

In this situation, N_Heads is the "measure." It is a statistic that describes the whole coins collection. Here is a picture of what this example might look like.