Shoelace formula for polygonal area: Difference between revisions
→{{header|Python}}: Added a variant in terms of reduce and cycle
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(→{{header|Python}}: Added a variant in terms of reduce and cycle) |
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30.0
>>> </lang>
Or, defined in terms of '''reduce''' and '''cycle''':
{{Trans|Haskell}}
{{Works with|Python|3}}
<lang python>'''Shoelace formula for polygonal area'''
from itertools import (cycle, islice)
from functools import (reduce)
# shoelaceArea :: [(Float, Float)] -> Float
def shoelaceArea(xys):
'''Area of polygon with vertices
at (x, y) points in xys.'''
def go(a, tpl):
(x, y), (dx, dy) = tpl
l, r = a
return (l + x * dy, r + dx * y)
(nl, nr) = reduce(
go,
zip(xys, tail(cycle(xys))),
(0, 0)
)
return abs(nl - nr) / 2
# TEST -------------------------------------------------
# main :: IO()
def main():
'''Test'''
print(
shoelaceArea(
[(3, 4), (5, 11), (12, 8), (9, 5), (5, 6)]
)
)
# GENERIC -------------------------------------------------
# tail :: [a] -> [a]
# tail :: Gen [a] -> [a]
def tail(xs):
'''The elements following the head of a
(non-empty) list or generator stream.'''
if isinstance(xs, list):
return xs[1:]
else:
list(islice(xs, 1)) # First item dropped.
return xs
if __name__ == '__main__':
main()</lang>
{{Out}}
<pre>30.0</pre>
=={{header|Racket}}==
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