python dict, find value closest to x

Question

say I have a dict like this :

d = {'a': 8.25, 'c': 2.87, 'b': 1.28, 'e': 12.49}

and I have a value

v = 3.19

I want to say something like :

x = "the key with the value CLOSEST to v"

Which would result in

x = 'c'

Any hints on how to approach this?

Answer 1

Use min(iter, key=...)

target = 3.19
key, value = min(dict.items(), key=lambda (_, v): abs(v - target))

Answer 2

You can do this:

diff = float('inf')
for key,value in d.items():
    if diff > abs(v-value):
        diff = abs(v-value)
        x = key

print x

which gives 'c'

You can also use min to do the job:

x = min(((key, abs(value-v)) for key,value in d.items()), key = lambda(k, v): v)[0]

Answer 3

Not sure what you want it to do if two values are equally far from the target, but if that's ever an issue, you could use something like this

min_diff = min(abs(v - target) for v in d.values())
closest_keys = [k for k, v in d.items() if abs(v - target) == min_diff]

Answer 4

for python3, use this:

target = 3.19    
key, value = min(d.items(), key=lambda kv : abs(kv[1] - target))

if you just want the key of the value that's closest to target:

value = min(d.items(), key=lambda kv : abs(kv[1] - target))[0]