How can I create an array by concatenating from 2 arrays?

Question

I have these two arrays

slist = np.arange(1,1723,50) #List of start index
elist = np.arange(50,1800,50) #End index

This

   'G'+'{:0>5}'.format(slist[0])+"-"+'{:0>5}'.format(elist[0])

gives me:

    'G00001-00050'

I want to do this over all the elements of slist and elist.

How can I do this?

The idea is to construct a array list which I'll use to import files which have them as strings in file names

akuiper · Accepted Answer · 2017-10-21 00:04:59Z

1

You can use np.char.zfill to pad 0 to strings and np.char.add to concatenate them element-wise:

from functools import reduce
import numpy as np

def cust_format(slist, elist):

    slist = np.char.zfill(slist.astype(str), 5)
    elist = np.char.zfill(elist.astype(str), 5)
    lst = ['G', slist, '-', elist]

    return reduce(np.char.add, lst)

cust_format(slist, elist)
#array(['G00001-00050', 'G00051-00100', 'G00101-00150', 'G00151-00200',
#       'G00201-00250', 'G00251-00300', 'G00301-00350', 'G00351-00400',
#       'G00401-00450', 'G00451-00500', 'G00501-00550', 'G00551-00600',
#       'G00601-00650', 'G00651-00700', 'G00701-00750', 'G00751-00800',
#       'G00801-00850', 'G00851-00900', 'G00901-00950', 'G00951-01000',
#       'G01001-01050', 'G01051-01100', 'G01101-01150', 'G01151-01200',
#       'G01201-01250', 'G01251-01300', 'G01301-01350', 'G01351-01400',
#       'G01401-01450', 'G01451-01500', 'G01501-01550', 'G01551-01600',
#       'G01601-01650', 'G01651-01700', 'G01701-01750'], 
#      dtype='|S12')

answered Oct 21, 2017 at 0:04

akuiper

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3 Comments

PeterH Over a year ago

I might be misunderstanding the question but what I got is that they are looking to have every element in slist used with every element from elist. This will result in 1225 elements total in the final list. It appears that your function is returning 35.

akuiper Over a year ago

@PeterH It is possible that OP wants an outer concatenation. Maybe OP will clarify later.

maximusdooku Over a year ago

Yes, @Psidom is correct. I actually didn't know the term for it.

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