Slicing numpy with condition

Question

I have numpy array with the sape of 178 rows X 14 columns like this:

       0      1     2     3     4      5     6     7     8     9      10    11  \
0    1.0  14.23  1.71  2.43  15.6  127.0  2.80  3.06  0.28  2.29   5.64  1.04   
1    1.0  13.20  1.78  2.14  11.2  100.0  2.65  2.76  0.26  1.28   4.38  1.05   
2    1.0  13.16  2.36  2.67  18.6  101.0  2.80  3.24  0.30  2.81   5.68  1.03   
3    1.0  14.37  1.95  2.50  16.8  113.0  3.85  3.49  0.24  2.18   7.80  0.86   
4    1.0  13.24  2.59  2.87  21.0  118.0  2.80  2.69  0.39  1.82   4.32  1.04   
..   ...    ...   ...   ...   ...    ...   ...   ...   ...   ...    ...   ...   
173  3.0  13.71  5.65  2.45  20.5   95.0  1.68  0.61  0.52  1.06   7.70  0.64   
174  3.0  13.40  3.91  2.48  23.0  102.0  1.80  0.75  0.43  1.41   7.30  0.70   
175  3.0  13.27  4.28  2.26  20.0  120.0  1.59  0.69  0.43  1.35  10.20  0.59   
176  3.0  13.17  2.59  2.37  20.0  120.0  1.65  0.68  0.53  1.46   9.30  0.60   
177  3.0  14.13  4.10  2.74  24.5   96.0  2.05  0.76  0.56  1.35   9.20  0.61

    12      13  
0    3.92  1065.0  
1    3.40  1050.0  
2    3.17  1185.0  
3    3.45  1480.0  
4    2.93   735.0  
..    ...     ...  
173  1.74   740.0  
174  1.56   750.0  
175  1.56   835.0  
176  1.62   840.0  
177  1.60   560.0  

[178 rows x 14 columns]

I tried to print it in dataframe for all the rows and only the first (index 0) column and the output worked like this:

     0
0    1.0
1    1.0
2    1.0
3    1.0
4    1.0
..   ...
173  3.0
174  3.0
175  3.0
176  3.0
177  3.0

[178 rows x 1 columns]

using the same logic, I want totake all the rows and only the first column with the value is below 2. I tried to do it like this and it doesn't work:

reduced = data[data[:,0:1]<=2]

I got an

IndexError

like this:

IndexError                                Traceback (most recent call last)
<ipython-input-159-7eab0abd8f99> in <module>()
----> 1 reduced = data[data[:,0:1]<=2]

IndexError: boolean index did not match indexed array along dimension 1; dimension is 14 but corresponding boolean dimension is 1.

anybody can help me? thank in advance

Answer 1

Solved it.

It is just as simple as just convert the numpy array to dataframe and then select rows based on condition in dataframe:

reduced = data[data['class'] <= 2]