Python: get the corresponding key from value

Question

def get_nearest_less_element(d, k):
    return (min(value for value in map(float, d.values()) if value >= k))

So, d is a dict() and k is float, this function returns me the correct value, but can I return the corresponding key of that value from this function?

Simply iterate over the dictionary using d.items(), and there you have access to key and value. At the end, you would have both key and value. Return them as a tuple. — vb_rises, Sep 10 '19 at 01:24
Possible duplicate of [Finding key from value in Python dictionary:](https://stackoverflow.com/questions/7657457/finding-key-from-value-in-python-dictionary) — Mars, Sep 10 '19 at 01:26
The title question is a duplicate, the thing you actually want to know is how to iterate key AND value, which is a different question — Mars, Sep 10 '19 at 01:28

score 5 · Accepted Answer · answered Sep 10 '19 at 01:25

5

def get_nearest_less_element(d, k):
    return min(key for key, value in d.items() if float(value) >= k)

answered Sep 10 '19 at 01:25

Deepstop

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Olivier Melançon · Answer 2 · 2019-09-10T01:33:29.433

4

Instead of iterating over values with dict.values(), iterate over both keys and values with dict.items() which yields (key, value) pairs.

def get_nearest_less_element(d, k):
    return min(key for key, value in d.items() if float(value) >= k)

edited Sep 10 '19 at 01:33

answered Sep 10 '19 at 01:26

Olivier Melançon

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score 1 · Answer 3 · answered Sep 10 '19 at 01:57

If key is what you want:

def get_nearest_less_element(dict_obj, threshold):
    min_value, min_key = min(
        ((value, key) for key, value in dict_obj.items() if float(value) < threshold),
        key=lambda value_key: float(value_key[0])
    )
    print('min_value =', min_value, ', min_key =', min_key)
    return min_key

Basically, what I did is similar to @MrRobot9, but I sorted the pairs of (value, key) based on the values. Note that because I put the value before the key, the sorting will be based on value, there is no need for the key= part, but I just put it there to be more explicit.

score 0 · Answer 4 · answered Sep 10 '19 at 02:18

If you want to return the neighbor's , consider this solution:

def get_nearest_less_element2(d, k):
    dict_nearest = {value:key for key,value in d.items() if value >= float(k)}
    nearest_index = min(dict_nearest)
    nearest_value = dict_nearest[nearest_index]
    return nearest_index, nearest_value

Moreover, with the following simple test you can check the equivalence of the results obtained from your old function and the new one:

d={1:11, 100:333, 40:44, 9:21, 4:99, 88:31, 7:77}
test_res = []

for k in range(0, 100, 5):
    test_res.append(get_nearest_less_element(d,k) == get_nearest_less_element2(d,k)[0])

print(all(test_res))
# True

Python: get the corresponding key from value

4 Answers4