I'm a beginner and I want to create a matrix. For example:
0 1 1
1 1 1
1 1 2
irb(main):001:0> t = [[1]*3]*3
=> [[1, 1, 1], [1, 1, 1], [1, 1, 1]]
irb(main):002:0> (0...3).each do |x| t[x][x]=x end
=> 0...3
irb(main):003:0> t
=> [[0, 1, 2], [0, 1, 2], [0, 1, 2]] # why all values changed?
What's wrong?
The way you construct the array does not cretae new arrays for each row but references the same array for all rows:
t.each do |row|
p row.object_id
end
# 70325094342320
# 70325094342320
# 70325094342320
It is the same as:
a = [1, 1, 1]
t = [a, a, a]
Try this to see the difference:
t = [[1] * 3, [1] * 3, [1] * 3]
