Duplicating Array Python

Question

I would like to duplicate an array inside the array to account for a duplicated separate array. The data I have is for thousands of numbers but for simplification, this is what I'm looking for:

a = [1,2,3,4,5]
b = [2,6,5,7,3]

new_a = [1,2,3,4,5,1,2,3,4,5]
new_b = [2,6,5,7,3,2,6,5,7,3]

#array b
magnitude = data[:,1]

# phaseresult_i is array a

for t in range(len(time)):
    floor = math.floor((time[t]-time[0])/(bestperiod))
    phase_i = ((time[t]-time[0])/(bestperiod))-floor
    phaseresult_i.append(phase_i)

newphaseresult_i = phaseresult_i +phaseresult_i
newmagnitude = magnitude + magnitude

Above is what I have exactly in my code, and the length of the first array doubles but the length of the second array does not.

to account for a duplicated separate array What does that mean? — jpp
– jpp, Commented Oct 24, 2018 at 15:39
@jpp Duplicate both arrays so they match the original array values according to the index — hlku2334
– hlku2334, Commented Oct 24, 2018 at 15:50
Your edit make the post not be in accordance with Minimal, Complete, and Verifiable example standards — Hemerson Tacon
– Hemerson Tacon, Commented Oct 24, 2018 at 15:59

Hemerson Tacon · Accepted Answer · 2018-10-24 15:39:15Z

1

Just use the + operator:

a = [1,2,3,4,5]
b = [2,6,5,7,3]

new_a = a + a
new_b = b + b

answered Oct 24, 2018 at 15:39

Hemerson Tacon

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5 Comments

hlku2334 Over a year ago

For my "a" the array duplicated, but for my "b" the array did not.

Hemerson Tacon Over a year ago

What has in b after doing this?

hlku2334 Over a year ago

so I have len(a) = 1325, len(a_new)=2650, len(b)=1325, len(b_new)=1325. I've edited my original post to show what my a and b arrays are

Hemerson Tacon Over a year ago

Please, double check your code. It's a prety straight forward operation. a and b are list of integers as in your example, right?

hlku2334 Over a year ago

I added a+a and b+b. Please see above.

Mäne · Accepted Answer · 2018-10-24 15:47:42Z

1

You can use the + operator:

a = [1,2,3,4,5]
b = [2,6,5,7,3]
new_a = a+a 
new_b = b+b 

print(new_a) #[1, 2, 3, 4, 5, 1, 2, 3, 4, 5]
print(new_b) #[2, 6, 5, 7, 3, 2, 6, 5, 7, 3]

answered Oct 24, 2018 at 15:47

Mäne

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Comments

roganjosh · Accepted Answer · 2018-10-24 15:49:50Z

1

You could do it lazily with an itertools recipe assuming that you wanted to repeat the concatenation more than once (but it still works if you set n=2 for a single repeat).

from itertools import chain, repeat

def ncycles(iterable, n):
    "Returns the sequence elements n times"
    return chain.from_iterable(repeat(tuple(iterable), n))

a = [1,2,3,4,5]
b = ncycles(a, 3)

Then either call list() on b or iterate through it. For large arrays this will be more efficient, and it's a bit more convenient than using + concatenation.

edited Oct 24, 2018 at 15:49

answered Oct 24, 2018 at 15:44

roganjosh

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Comments

jsones · Accepted Answer · 2018-10-24 15:39:54Z

0

You can simply add the old array to itself.

new_a = a + a
new_b = b + b

answered Oct 24, 2018 at 15:39

jsones

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Joe Hinton · Accepted Answer · 2018-10-24 15:43:43Z

0

The + operator will work if you are looking to create a new variable.

a = [1,2,3,4,5]
b = [2,6,5,7,3]

new_a = a + a
new_b = b + b

Alternatively if you wish to just change the list in place you could use .extend

a = [1,2,3,4,5]
b = [2,6,5,7,3]

a.extend(a)
b.extend(b)

answered Oct 24, 2018 at 15:43

Joe Hinton

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