3D array to 2d array from pandas Python and Numpy

Question

I have created the array from a csv using pandas and numpy. This is my code that convert 2D csv to 3D array:

>>> import pandas as pd
>>> import numpy as npp
>>> df = pd.read_csv("test.csv")
>>> df_mat = df.values
>>> seq_len = 3
>>> data=[]
>>> for index in range(len(df_mat) - seq_len):
...     data.append(df_mat[index: index + seq_len])
...
>>> data = np.array(data)
>>> data.shape
(4, 3, 9)

The csv is used is:

input1,input2,input3,input4,input5,input6,input7,input8,output
1,2,3,4,5,6,7,8,1
2,3,4,5,6,7,8,9,0
3,4,5,6,7,8,9,10,-1
4,5,6,7,8,9,10,11,-1
5,6,7,8,9,10,11,12,1
6,7,8,9,10,11,12,13,0
7,8,9,10,11,12,13,14,1

Now I want to get the 3D array back to 2D array format.
Kindly, let me know how I can I do that. Not getting any clue.

Think that should be - for index in range(len(df_mat) - seq_len + 1): instead to cover all subarrays? — Divakar
– Divakar, Commented Feb 21, 2019 at 11:19

Divakar · Accepted Answer · 2019-02-21 11:19:27Z

1

Slice on the 0th rows along each each block until the last block and stack with the last one -

np.vstack((data[np.arange(data.shape[0]-1),0],data[-1]))

Output with given sample data -

In [24]: np.vstack((data[np.arange(data.shape[0]-1),0],data[-1]))
Out[24]: 
array([[ 1,  2,  3,  4,  5,  6,  7,  8,  1],
       [ 2,  3,  4,  5,  6,  7,  8,  9,  0],
       [ 3,  4,  5,  6,  7,  8,  9, 10, -1],
       [ 4,  5,  6,  7,  8,  9, 10, 11, -1],
       [ 5,  6,  7,  8,  9, 10, 11, 12,  1],
       [ 6,  7,  8,  9, 10, 11, 12, 13,  0],
       [ 7,  8,  9, 10, 11, 12, 13, 14,  1]], dtype=int64)

Or slice 0th rows across all blocks and stack with the last block skipping the first row -

In [28]: np.vstack((data[np.arange(data.shape[0]),0],data[-1,1:]))
Out[28]: 
array([[ 1,  2,  3,  4,  5,  6,  7,  8,  1],
       [ 2,  3,  4,  5,  6,  7,  8,  9,  0],
       [ 3,  4,  5,  6,  7,  8,  9, 10, -1],
       [ 4,  5,  6,  7,  8,  9, 10, 11, -1],
       [ 5,  6,  7,  8,  9, 10, 11, 12,  1],
       [ 6,  7,  8,  9, 10, 11, 12, 13,  0],
       [ 7,  8,  9, 10, 11, 12, 13, 14,  1]], dtype=int64)

answered Feb 21, 2019 at 11:19

Divakar

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5 Comments

Jaffer Wilson Over a year ago

I am not getting the last row sir. How you are getting it I didn't got that.

Divakar Over a year ago

@JafferWilson Read my comment?

Jaffer Wilson Over a year ago

Thank you for the insights sir.

Jaffer Wilson Over a year ago

Sir, can you please help me on these question as well: stackoverflow.com/questions/54789287/… and ai.stackexchange.com/questions/10781/…? From your profile I guess you can help me.

Divakar Over a year ago

@JafferWilson Sorry mate, don't think I have the expertise on those tags.

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