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+--- Thread: getting previous/next valid value in a list, cyclically (/thread-9064.html)
getting previous/next valid value in a list, cyclically - studeo - Mar-19-2018
I have a list of values... some are valid, some invalid (containing None). I test each element for validity. When I find an invalid element, I need to find indexes of the closest previous and the closest next valid value. I need to treat the list as a cycle, so if there are no valid elements before/after the initial element, it should search from the end/start of the list... This way, if there is at least one valid value in the list, both the previous and the next valid value will be found (it can be the same index, if there is only one valid value in the list).
I am able to solve it, but with a ridiculously complicated code. Could you help me find some elegant solution? I am not a programmer, just using my very humble programming skills to process data in another field.
RE: getting previous/next valid value in a list, cyclically - micseydel - Mar-19-2018
Can you post what you've tried, and some sample uses of the code?
RE: getting previous/next valid value in a list, cyclically - studeo - Mar-19-2018
example_values = [None, None, 2, None, 4, None, None, 7, None, None]
for i, v in enumerate(example_values):
if v is not None:
print("value at position {} is valid: {}".format(i,v))
else:
print("value at position {} is invalid".format(i))
prev_valid = False
next_valid = False
for j, w in enumerate(example_values):
if j < i and w is not None:
prev_valid = j
if not prev_valid:
for j, w in enumerate(example_values):
if w is not None:
prev_valid = j
for j, w in enumerate(example_values):
if j > i and w is not None:
next_valid = j
break
if not next_valid:
for j, w in enumerate(example_values):
if w is not None:
next_valid = j
break
print(" previous valid value is at position {}".format(prev_valid))
print(" next valid value is at position {}".format(next_valid))
RE: getting previous/next valid value in a list, cyclically - micseydel - Mar-19-2018
Can you give a very, very simplified example of what you want? It seems extremely complex right now, and I'm not sure if it's because of the requirements or the implementation.
RE: getting previous/next valid value in a list, cyclically - Gribouillis - Mar-19-2018
You can use module bisect
import bisect as bs
def valid_indexes(seq):
return [i for i, v in enumerate(seq) if v is not None]
def prev_valid(valid, i):
return valid[bs.bisect_left(valid, i) - 1]
def next_valid(valid, i):
return valid[bs.bisect_right(valid, i) % len(valid)]
if __name__ == '__main__':
example_values = [None, None, 't', None, 'f', None, None, 's', None, None]
valid = valid_indexes(example_values)
for i, v in enumerate(example_values):
if v is not None:
print("value at position {} is valid: {}".format(i,v))
else:
print("value at position {} is invalid".format(i))
print(" previous valid value is at position {}".format(prev_valid(valid, i)))
print(" next valid value is at position {}".format(next_valid(valid, i)))
RE: getting previous/next valid value in a list, cyclically - studeo - Mar-20-2018
(Mar-19-2018, 11:03 PM)Gribouillis Wrote: You can use module bisect
Thanks! Works perfectly.