Repeated rows in a numpy array

Question

I feel like I'm going insane because I can't figure out what feels like should be a simple problem! I want to generate fake data in a numpy array and I can't figure out how to repeat a row of observations. I'd rather generate thousands of rows and I can't figure out how to repeat a row whenever I feel like.

For example, here's my current code:

voters = np.array(
    [
        ['Democrat', 'Republican', 'Third'],
        ['Democrat', 'Republican', 'Third'],
        ['Democrat', 'Republican', 'Third'],
        ['Democrat', 'Republican', 'Third'],
        ['Democrat', 'Republican', 'Third'],
        ['Democrat', 'Third', 'Republican'],
        ['Democrat', 'Third', 'Republican'],
        ['Democrat', 'Third', 'Republican'],
        ['Democrat', 'Third', 'Republican'],
    ]
)

But I just want to be able to condense this. It's obviously not manageable to make large datasets this way!

Thank you

Do you want to generate thousands of identical rows or should each row be randomly ordered? — pho
– pho, Commented Nov 23, 2022 at 15:06

obchardon · Accepted Answer · 2022-11-23 15:23:31Z

4

Use np.repeat():

voters = np.array([['row1', 'row1', 'row1'],
                   ['row2', 'row2', 'row2']])

# We repeat 2 times the first row and 4 times the second row.
np.repeat(voters,[2,4],axis=0)
# voters.repeat([2,4],axis=0) produce the same result.

And we obtain:

array([['row1', 'row1', 'row1'],
       ['row1', 'row1', 'row1'],
       ['row2', 'row2', 'row2'],
       ['row2', 'row2', 'row2'],
       ['row2', 'row2', 'row2'],
       ['row2', 'row2', 'row2']])

edited Nov 23, 2022 at 15:23

answered Nov 23, 2022 at 15:15

obchardon

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1 Comment

rulesforpower Over a year ago

Oh my gosh I had visited that page before but had a complete misunderstanding of how its syntax worked. This is it--thank you!

robinood · Accepted Answer · 2022-11-23 14:55:37Z

1

You can use this:

np.array([['Democrat', 'Republican', 'Third']]* 10000)

to generate as many duplicate rows as you want.

answered Nov 23, 2022 at 14:55

robinood

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2 Comments

rulesforpower Over a year ago

How do I do this for multiple lines? Because ''' voters = np.array( [['Democrat', 'Republican', 'Thurd']] * 10, [['Democrat', 'Third', 'Republican']] * 4 ) voters ''' just gets me a type error

robinood Over a year ago

Please have a look at @obchardon's answer. it answers your comment

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