Currently Coda doesn’t allow me to reference more than 2 columns when I am trying to do the sum. So I added some more temp (hidden) columns to do the sum in parts and them combine it in two steps …
You can use the ‘Scale’ type column instead of checkbox. Set the max value to 1, and then these will function as numbers which can be summed as opposed to boolean values (true/false).
The other option, if you want to stick with checkboxes, is to nest several if()'s into your formula like so:
sum(if(thisRow.1,1,0),if(thisRow.2,1,0))...
This way you are converting each boolean to an integer. Hope this helps!