I have two lists of dictionaries.
foo = [{'Tom': 8.2}, {'Bob': 16.7}, {'Mike': 11.6}]
bar = [{'Tom': 4.2}, {'Bob': 6.7}, {'Mike': 10.2}]
The subtraction of a and b should be updated in foo:
foo = [{'Tom': 4.0}, {'Bob': 10.0}, {'Mike': 1.4}]
Now I tried this with two loops and the zip
-function:
def sub(a,b):
for mydict,mydictcorr in zip(a,b):
{k:[x-y for x, y in mydict[k], mydictcorr[k]] for k in mydict}
return mydict
print sub(foo,bar)
I get a TypeError: 'float' object is not iterable
. Where's my mistake?
You were very close. The issue was the list comprehension you had in your dictionary comprehension. mydict[k], mydictcorr[k]
were both returning floats, but you were trying to iterate over them [x-y for x, y in mydict[k], mydictcorr[k]]
.
This will work for you:
def sub(base, subtract):
corrected = []
for base_dict, sub_dict in zip(base, subtract):
corrected.append({k: v - sub_dict.get(k, 0) for k, v in base_dict.items()})
return corrected
Or as a much less readable one-liner (because I wanted to see if I could):
def sub(base, subtract):
return [{k: v - sub_dict.get(k, 0) for k, v in base_dict.items()} for base_dict, sub_dict in zip(base, subtract)]
Having said that, you may still see some weird results when you subtract floats. Eg, {'Tom': 3.999999999999999}
. You may want to wrap v - sub_dict.get(k, 0)
in a call to round.
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