Find row closest value to input

Question

I am struggling with this problem. I have an pandas array which looks like this

               delta_n    column_1   ...
0                10      10        ...
1                20       0
2                30       0

Now i have a number, lets say i search for delta_n=20.5 and I want to select the row closest to the number of delta_n.

My output should be:

1                20       0

I tried it with df.loc[20.5] but as it is not in the pd dataframe it doesn't work.

Thanks, R

Answer 1

Subtract value by sub, get absolute values by abs, find index with minimal value by idxmin and last select by loc:

idx = df['delta_n'].sub(delta_n).abs().idxmin()

#added double [[]] for one row DataFrame
df1 = df.loc[[idx]]
print (df1)
   delta_n  column_1
1       20         0

#output Series with one []
s = df.loc[idx]
print (s)
delta_n     20
column_1     0
Name: 1, dtype: int64

Details:

print (df['delta_n'].sub(delta_n))
0   -10.5
1    -0.5
2     9.5
Name: delta_n, dtype: float64

print (df['delta_n'].sub(delta_n).abs())
0    10.5
1     0.5
2     9.5
Name: delta_n, dtype: float64

print (df['delta_n'].sub(delta_n).abs().idxmin())
1

Another numpy solution for positions by numpy.argmin and selecting by iloc:

pos = df['delta_n'].sub(delta_n).abs().values.argmin()
print (pos)
1

df1 = df.loc[[pos]]
print (df1)
   delta_n  column_1
1       20         0

s = df.loc[pos]
print (s)
delta_n     20
column_1     0
Name: 1, dtype: int64