I have a python2 code that I used before but I would like replace reduce by a loop. How can I rewrite this part prod = reduce(lambda a, b: a * b, n) function below?
def chineeseRemainder(n, a):
sum = 0
prod = reduce(lambda a, b: a * b, n)
for n_i, a_i in zip(n, a):
p = prod // n_i
sum += a_i * Get_Multi_Inv(p, n_i) * p
return sum % prod
In general for a reduce() without a starting value, you can use iter and next to convert it to a for loop. This combination lets you use the first element of the iterable as the starting accumulator value, and loop over the rest.
iterator = iter(n)
prod = next(iterator)
for x in iterator:
prod *= x
But in the specific case of multiplication, we know the identity element is 1, so we can use that as the starting value and multiply the whole iterable.
prod = 1
for x in n:
prod *= x
Not all functions will have an identity like this, but many do, like 0 for + and math.inf for min(), etc.
you can also add import
from functools import reduce
I have it working.
def reduce(function, iterable, initializer=None):
it = iter(iterable)
if initializer is None:
value = next(it)
else:
value = initializer
for element in it:
value = function(value, element)
return value
and I called it the function above with
prod = reduce(function1, n)
reduce function, why not use the one builtin? You can use six as a compatibility layer. The benefit of not using reduce is readability (and possibly one less func call); this solution eschews both of those benefits.