I have an array of floats (size 9300), and another array of ints (size 2600) with indexes of the first array. I am trying to get the values in the first array based on the index in the second array. Example:
index 1st_array
0 12.00
1 3.89
2 24.20
3 34.60
index 2nd_array
0 0
1 2
The output:
index 3nd_array
0 12.00
1 24.20
Edit: those are actually numpy arrays:
a1 = np.array([12.00, 3.89, 24.20, 34.60])
a2 = np.array([0, 2])
import numpy as np
arr1 = np.array([12.00, 3.89, 24.20, 34.60])
arr2 = np.array([0, 2])
print(arr1[arr2])
prints
[12. 24.2]
If you have two Series s1 and s2, use:
s1.loc[s2]
Example:
s1 = pd.Series(['a', 'b', 'c', 'd'])
s2 = pd.Series([0, 2])
s1.loc[s2]
0 a
2 c
dtype: object
For numpy arrays
a1[a2]
Example:
a1 = np.array(['a', 'b', 'c', 'd'])
a2 = np.array([0, 2])
a1[a2]
array(['a', 'c'], dtype='<U1')
For DataFrames:
df1.set_index('index').loc[df2['2nd_array']].reset_index()
NB. the set_index/reset_index are only required if "index" are columns
Example:
df1 = pd.DataFrame({'index': [0, 1, 2, 3],
'1st_array': [12.0, 3.89, 24.2, 34.6]})
df2 = pd.DataFrame({'index': [0, 1],
'2nd_array': [0, 2]})
(df1
.set_index('index')
.loc[df2['2nd_array']]
.reset_index()
)
index 1st_array
0 0 12.0
1 2 24.2
