How to split the results of formulas in one cell over multiple columns in Google Spreadsheets?

Another approach:

=FILTER({A2:A4,SUM(1,3)*ROW(A2:A4)^0},C2:C4=TRUE)

EXPLANATION:

FILTER can take an array as its first argument. The tricky part is that every element of that array must have the same dimensions. While A2:A4 is a 3x1 range, SUM(1,3) is a 1x1 range. But this can be solved by multiplying SUM(1,3) by a sort of placeholder 3x1 array: ROW(A2:A4)^0. Since every element in A2:A4 has a row number, and any number to the zero power (^0) is 1, this just signals Google Sheets to give you SUM(1,3) "multiplied by 1 for three rows. And that makes the two elements of that curly-bracket array match up with everything else.

You can use the following formula instead:

=ArrayFormula(SPLIT(FILTER(A2:A4&","&SUM(1,3),C2:C4=TRUE),","))

Functions used:

• ArrayFormula
• SPLIT
• FILTER
• SUM