CODEWITHSUNDEEP
pythonnumpy
Kien Mathias
Kien Mathias

Reputation: 19

returning the element in one list based on the index and maximum value of an element in another list

I have a list of lists which I converted into a numpy array:

lsts = ([[1,2,3], ['a','b','a']],
        [[4,5,6,7], ['a','a','b','b']], 
        [[1,2,3],['b','a','b']])

np_lsts = np.array(lsts)

I want to return the largest element in the first list where a 'b' occurs in the second list. I think I have to use indexes but am stuck!

i.e. I want to return (2, 7, 3) in this case

Upvotes: 0

Views: 93

Answers (5)

Ohad Eytan
Ohad Eytan

Reputation: 8464

That will do:

[max(u for u,v in zip(x,y) if v=='b') for x,y in lsts if 'b' in y]

Using zip() and max() in a nested list comprehension

Upvotes: 1

BPL
BPL

Reputation: 9863

One possible solution to your problem:

lsts = ([[1, 2, 3], ['a', 'b', 'a']],
        [[4, 5, 6, 7], ['a', 'a', 'b', 'b']],
        [[1, 2, 3], ['b', 'a', 'b']],
        [[1, 2, 3], ['a']]
        )

result = []
for l in lsts:
    indices = [l[0][index] for index, v in enumerate(l[1]) if v == 'b']
    if indices:
        result.append(max(indices))

print result

Upvotes: 1

Eelco Hoogendoorn
Eelco Hoogendoorn

Reputation: 10759

This should be a lot more efficient than the current solutions if the sublists have a lot of elements, since it is vectorized over those sublists:

import numpy_indexed as npi
results = [npi.group_by(k).max(v) for v,k in lsts]

Upvotes: 0

Craig Burgler
Craig Burgler

Reputation: 1779

def get_max(l):
    first = True
    for e1, e2 in zip(l[0], l[1]):
        if e2 == 'b' and first:
            max = e1
            first = False
        elif e2 == 'b' and e1 > max:
            max = e1
    return max

result = ()
for l in lsts:
    if 'b' in l[1]:
        result += (get_max(l),)
print(result)

Upvotes: 0

Irfan434
Irfan434

Reputation: 1681

The following function returns a result list. If needed, you could return a tuple instead of a list.

def maxNum(lsts, character):
    result = []
    for entry in lsts:
        if character in entry[1]:
            result.append(max(entry[0]))
    return result

# lsts = ... # (put lsts here)

print maxNum(lsts, 'b')

Upvotes: 1

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