Mark items based on criteria

I have a table in Excel 2013 that contains categories as rows and items as columns. An X in the intersection of a category and item means that the item belongs to the category.

On another sheet I have a list of all items. I would like to highlight all items (or add an X in the adjacent column) that belong to a certain category.

Categories | Item1 | Item2 | Item 3
-----------------------------------
Category 1 |       |   X   |
Category 2 |       |   X   |   X
Category 3 |   X   |   X   |   X
Category 4 |       |       |
Category 5 |   X   |       |   X

Selected: Category 5

Items | In category
-------------------
Item1 |      X
Item2 |      
Item3 |      X     <- ?

What is the formula for the cell, the ? is pointing towards?

You can use the INDEX function to get the information from a particular set of coordinates.

For example, in this case, we'd get the value for the cell in the 5th row and the 1st column of the selected area:

If we want to dynamically find those values, we can use MATCH to find the column or row number corresponding to our value like this:

=INDEX($B$2:$D$6,5,MATCH($A10,$B$1:$D$1,0))

In this case the column number is dynamically pulled based on the item you're on. The row number is hardcoded as row 5, but you can use the same technique to pull in a row number

The end result should look like this: