Lookup closest value in Pandas DataFrame
Not sure if this will help, but I'm using this to find nearest in a sorted column: (time series stuff)

result_index = df['col_to_search'].sub(search_value).abs().idxmin()


.sub(search_value) subtracts search_value from the df[col_to_search] to make the nearest value almost-zero,
.abs() makes the almost-zero the minimum of the column,
.idxmin() yields the df.index of the minimum value, or the closest match to search_value.

I got this approach from a similar search, but didn't note the original author or the site I found it.