I am new to Sage, so please help me understand the following: How come
map(lambda x: mod(x,2),[4,3,2,1,1])returns the perfectly sane answer [0,1,0,1,1]
but trying to compute the sum
sum(map(lambda x: mod(x,2),[4,3,2,1,1]))gives the value 1, and not 3. Somehow, it seems that sage thinks that I wish to apply the inner lambda again on the result of the sum.
You can try
map(lambda x: x%2,[4,3,2,1,1])then
sum(map(lambda x: x%2,[4,3,2,1,1]))will return the desired output.
What happens when you use mod(x,2) is that sage returns an element of Z2, however the % operator returns an Integer.
To put it another way, that means that the sum of `mod(x,2)` being either zero or one is a feature, not a bug!
I would prefer comprehension sum(x%2 for x in [4,3,2,1,1]) rather than map.
Aha! Cool! That makes sense.
Asked: 11 years ago
Seen: 900 times
Last updated: Jul 05 '13
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