Find variable closest to a value in a list

Question

I have a list of variables [A1, A2, A3, A4, A5, A6, A7, A8, A9, A10] to 1 decimal place. I have a variable B which can be any number to decimal place. I would like to find the closest value in the list to variable B. And return not the value but the A number(A5 for example).

Welcome Colin! What did you tried? Could you post your code and explain which problem do you have implementing this? — llrs, May 21 '15 at 12:02
Do you actually want the _name_ of the variable, or the index in the list? The former will generally not be (easily) possible, but you could use a dictionary and return the key. — tobias_k, May 21 '15 at 12:05
Breaking it down, you want the [index](https://docs.python.org/2/tutorial/datastructures.html) of the value in the list that has the least [difference](https://docs.python.org/2/library/functions.html#abs) to value B. Other hint: [for loop](https://wiki.python.org/moin/ForLoop) — Aeveus, May 21 '15 at 12:07

score 1 · Answer 1 · answered May 21 '15 at 12:23

from operator import itemgetter

a = [A1, A2, ........, A10]
minimum_list = [abs(variable - B) for variable in a]

return min(enumerate(minimum_list), key=itemgetter(1))[0]

This will return the index of the variable with the minimum difference.

return a[min(enumerate(minimum_list), key=itemgetter(1))[0]]

This will return the value in the list with the minimum difference with the variable B

score 0 · Answer 2 · answered May 21 '15 at 12:22

If you know numpy, you can write as this:

matA = array([A1, A2, A3, A4, A5, A6, A7, A8, A9, A10])
matB = array([B])
diff = abs(matA - matB)
minDiffValue = min(diff)

And then, write the code like this to find the index of the element:

closeValueIndex = []
index = 0
for i in diff:
    if i == minDiffValue:
        closeValueIndex.append(index)
    index += 1

score 0 · Answer 3 · edited Jun 23 '15 at 14:15

In [1]: vals = [0.8, 5.0, 10.2, 15.6]
        value = lambda myvalue: min(vals, key=lambda x: abs(x - myvalue))
        value(9.8)
Out[1]: 10.2

But if you want to return a non-numeric answer, to which I think you want. Just use the same but with a dictionary and the values as the keys, answers you want back as the values:

In [2]: vals = {0.8:'A1', 5.0:'A2', 10.2:'A3', 15.6:'A4'}
        value = lambda myvalue: vals.get(min(vals, key=lambda x: abs(x - myvalue)))
        value(9.8)
Out[2]: 'A3'

Find variable closest to a value in a list

3 Answers3