List of Lists
=============

A list is a sequence of items. In App Inventor, you create a list by using a ``make a list`` block, found in the Lists group. For example:

.. image:: list.png

A list of lists is a list whose elements are other lists. For example:

.. image:: list-of-lists.png

Often, the sublists only contain two items, and those items represent a key-value pair. In the list of lists shown above, "name" is a key and "Hello Kitty" is its value. In effect, a list of lists can be thought of as a lookup table. Conceptually, this is equivalent to a spreadsheet with two columns:

.. image:: spreadsheet.png

The ``look up in pairs`` block can be used to retrieve the value for a given key. For example, if we wanted to show Hello Kitty's height from the list of lists, we might do something like this:

.. image:: look-up-in-pairs.png


We prepared a project for you that demonstrates how the ``make a list`` and ``look up in pairs`` blocks work in practice. You can download :download:`HelloKittyFacts.aia`), make some changes, and run it on your phone to see how those changes affect the outcome.