Accumulation items in a table Options

[denmarks]

I have a table where one of the columns is activities. That field can contain any letters of the alphabet. There can be no duplicates within a cell but there can be none or any. There is a blank between each letter for readability. For example:
A C D F G
A B
[blank]
M N O R Z

What is the best way to scan the table and count how many of each letter appears? I assume creating an array and indexing by the letter may work best for the variables. I also need the best way to scan the table and the individual cell that would be compatible with multiple browsers.
Result
A - 2
B - 1
C - 1
etc