Function: primary_choice

--Usage--
> primary_choice(some_choice_value)

Returns the name of the 'top level' choice selected.

For example if a [[type:field|choice field]] is declared with the [[type:choice]]s:
>choice:
>	name: large
>	choice: red
>	choice: blue
>choice:
>	name: small
>	group choice: just small
>	choice: green
>	choice: yellow
Then @primary_choice("large red") == "large"@.

This function is used to keep [[type:statiscs_dimension|statistics]] cleaner by not having columns for all possible sub choices.

--Parameters--
! Parameter	Type			Description
| @input@	[[type:string]]		Choice value to look at.

--Examples--
> primary_choice("large red")    ==  "large"
> primary_choice("large")        ==  "large"
> primary_choice("small green")  ==  "small"