How do I find the closest values in a Pandas series to an input number?

Question

I have seen:

• how do I find the closest value to a given number in an array?
• How do I find the closest array element to an arbitrary (non-member) number?.

These relate to vanilla python and not pandas.

If I have the series:

ix   num  
0    1
1    6
2    4
3    5
4    2

And I input 3, how can I (efficiently) find?

1. The index of 3 if it is found in the series
2. The index of the value below and above 3 if it is not found in the series.

Ie. With the above series {1,6,4,5,2}, and input 3, I should get values (4,2) with indexes (2,4).

Answer 1

You could use argsort() like

Say, input = 3

In [198]: input = 3

In [199]: df.iloc[(df['num']-input).abs().argsort()[:2]]
Out[199]:
   num
2    4
4    2

df_sort is the dataframe with 2 closest values.

In [200]: df_sort = df.iloc[(df['num']-input).abs().argsort()[:2]]

For index,

In [201]: df_sort.index.tolist()
Out[201]: [2, 4]

For values,

In [202]: df_sort['num'].tolist()
Out[202]: [4, 2]

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Detail, for the above solution df was

In [197]: df
Out[197]:
   num
0    1
1    6
2    4
3    5
4    2