Jagged Arrays

The rows of a 2D array do not need the same length. A 2D array whose rows have different lengths is a jagged array. Here each row holds the scores of one player, and the players have played a different number of rounds:

var scores := [
	[90, 85, 70],
	[60],
	[75, 80]
]
print(scores[0].size()) # 3
print(scores[1].size()) # 1

In a jagged array, scores[0].size() is not the length of every row. Loop over the columns of the current row with scores[r].size():

for r in range(scores.size()):
	var total := 0
	for c in range(scores[r].size()):
		total += scores[r][c]
	print("Player ", r + 1, ": ", total)

Player 1: 245
Player 2: 60
Player 3: 155

A loop that always uses the length of the first row reads past the end of the shorter rows: scores[1][2] is an error, because row 1 has only index 0. for value in row always fits the row it walks through.

You build a jagged array like a grid, with a different length for each row. In this triangle, row r has r + 1 cells:

var triangle := []
for r in range(4):
	var row := []
	for c in range(r + 1):
		row.append("*")
	triangle.append(row)
for row in triangle:
	print("".join(row))

*
**
***
****

A row can even be empty: [[1, 2], [], [3]] is a valid jagged array with three rows.