Concatenate numpy array with list

Question

I want to concatenate numpy array with list. like this:

trainClass = np.ones(len(allDataList[0])).tolist()
trainArray = tfIdfsListTrain.toarray()
np.concatenate( (trainArray, trainClass))

but I don't know how do I do it.

Your array is numpy.array? Your list is named list? Please provide some sample data, and you better do not name your variables list, etc. — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Dec 28, 2017 at 19:18
What's the problem? Turn your list into an array and pass it to concatenate. Or let concatenate do it for you. If there is an error it probably has to do with a mismatch in shapes and dimensions. — hpaulj
– hpaulj, Commented Dec 28, 2017 at 19:24
@hpaulj shape of array is (2500, 8600) and len of list is 2500 — Mahsa
– Mahsa, Commented Dec 28, 2017 at 19:26

hpaulj · Accepted Answer · 2017-12-28 19:34:49Z

2

Sounds like your list, when turned into an array, doesn't have the right number of dimensions. Let me illustrate:

In [323]: arr = np.arange(12).reshape(3,4)
In [324]: alist = list(range(3))
In [325]: np.concatenate((arr,alist))
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-325-9b72583c40de> in <module>()
----> 1 np.concatenate((arr,alist))

ValueError: all the input arrays must have same number of dimensions
In [326]: arr.shape
Out[326]: (3, 4)

concatenate turns any list inputs into arrays:

In [327]: np.array(alist).shape
Out[327]: (3,)

arr is 2d, so this array needs to be 2d as well:

In [328]: np.array(alist)[:,None].shape
Out[328]: (3, 1)
In [329]: np.concatenate((arr, np.array(alist)[:,None]), axis=1)
Out[329]: 
array([[ 0,  1,  2,  3,  0],
       [ 4,  5,  6,  7,  1],
       [ 8,  9, 10, 11,  2]])

It is easy to concatenate a (3,4) array with a (3,1) array on the last dimension.

I get the impression that a lot of people are jumping into machine learning code (tensorflow, keras, sklearn) without understanding some of the basics of numpy arrays, such as shape and dimensions.

answered Dec 28, 2017 at 19:34

hpaulj

233k14 gold badges260 silver badges392 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

kRazzy R Over a year ago

your last comment is so true, earlier I was using everything as a black box to get ahead in the deep learing craze, but that got me no where, luckily I had a good mentor who is guiding me step by step. I'm thoroughly learning the basics before jumping into any deep learning.

Collectives™ on Stack Overflow

Concatenate numpy array with list

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related