These charts show information about the play along songs featured on UkeAlong.com. Most of these songs fall into the realm of Western pop and rock music. For reasons further outlined below these data should not be generalized, but you can get a good idea of which keys, chords and combinations of chords are the most essential to learn if you want to play this kind of music.
These data include all play along videos with chord information on songs in GCEA tuning. Different videos with the same song title and set of chords are counted once. The intention is to not count the same song twice, but there are some song versions re-tuned to a different key to make them easier to play on the ukulele with a different set of chords.
In these charts each chord has the same weight, i. e. a chord that occurs only on one beat in a particular song has the same weight as a chord that is played on 40 beats in that song. Moreover, chord information may be incomplete, inaccurate or incorrect. For example E7 may be suggested in play along videos although the actual chord played in the song is E.
With these caveats in mind, you certainly should not base a scientific thesis on these data, but it is safe to say that with learning the four chords C, G, F, and Am you'll be able to play along to a lot of popular songs. I do recommend though to keep adding new chords to your repertoire throughout your ukulele journey.