convert 1-D array to 2-D array

Question

How can I create a 2-d array from 1-d array in python?

Example :

     i/p 1-D array : [3,4,6]

Result :

     o/p 2-D array : [[3,], [4,], [6,]]

Or lets say a dataframe column with values = [3,4,6] as the 2-d above mentioned array.

Thanks in advance.

score -1 · Answer 1 · answered Oct 19 '18 at 11:03

-1

You can create an array for each element:

array = [3,4,6]
array2 = [[x] for x in array]
print(array2)

Try it online!

Or use map():

array = [3,4,6]
array2 = list(map(lambda x: [x], array))
print(array2)

Try it online!

answered Oct 19 '18 at 11:03

aloisdg

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Thanks.. that worked for list.. what about if its a 1-D numpy array or a dataframe column – AIMCognitiveGurgaon BigData Oct 19 '18 at 11:08
@AIMCognitiveGurgaonBigData read this: https://stackoverflow.com/questions/35215161/most-efficient-way-to-map-function-over-numpy-array#35215329 – aloisdg Oct 19 '18 at 11:10

score -1 · Accepted Answer · answered Oct 19 '18 at 11:13

You can use reshape to deal with numpy arrays. (Documentation)

Ex:

a = [1,2,3]
#reshaping a into 1 column and 3 rows
b = np.reshape(a,(3,1))

print(b)

to be more general you can just use the length of a as argument for the number of rows:

b = np.reshape(a,(len(a),1))

Note: As far as I know (someone correct me if I'm wrong), using numpy to deal with numpy arrays is faster. In other cases I suppose the list comprehension example would be the faster option.

convert 1-D array to 2-D array

2 Answers2