3 ms·

That groupBy doesn’t look like it does what you want to do. For example if “def fn(i): return i//2” You probably want to get an output like {0: [0,1]} but yo

That groupBy doesn’t look like it does what you want to do. For example if “def fn(i): return i//2” You probably want to get an output like {0: [0,1]} but you’ll only get a scalar for the value (1) and it will be the last one evaluated. It would be nice if there was a way to do this on one line but you’ll have to do ret=collections.defaultdict(list) For i In foo: ret[fn(i)].append(i) Return ret I suppose it isn’t that bad as it will be in the groupBy method. Or you could add it to a method on a list. I think that’s easier to do with Rust.

quietbritishjim 5y ago
Hmm, you're right... that one is actually quite hard to do in a Python-ish way. There is a one liner, just for the record, but it's absolutely horrific code because it redundantly re-evaluates the same conditions over and over: g = {fn(x): [y for y in foo if f(y)==f(x)] for x in foo} As you said, you'd have to use a for loop. I think sometimes people are unnecessarily afraid of for loops in Python (not everything has to fit on one line!) but this is a case it's a pity to take up so many lines. Or, back to square one, probably this is a case it's best just to use itertools groupby (after a sort) after all.