func:foldCols

foldCols(grid, colSelector, newColName, fn)

Fold a set of columns in each row into a new folded column and return a new grid. The columns to fold are selected by the colSelector function and removed from the result. The selector may be a list of string names or a function which takes a Col and returns true to select it. The folding function uses same semantics as fold().

Example:

// consider grid 'g' with the following structure:
a    b    c
---  ---  ---
1    10   100
2    20   200

// foldCols, add b and c together to create new bc column
g.foldCols(["b", "c"], "bc", sum)

// yields this grid:
a    bc
---  ---
1    110
2    220

// we could also replace list of col names with a function
colSel: col => col.name == "b" or col.name == "c"
g.foldCols(colSel, "bc", sum)