Create a string with every nth character of another string in Python

Question

I would like to split a string with the result being a string consisting only of every nth character of the original string. My first approach looks like this (and works):

#Divide the cipher text in the estimated number of columns
for i in range(0,keyLengthEstimator):
    cipherColumns.append(cipherstring[i])

for i in range(keyLengthEstimator,len(cipherstring)):
    if i % keyLengthEstimator == 0:
        cipherColumns[0] += cipherstring[i]
    elif i % keyLengthEstimator == 1:
        cipherColumns[1] += cipherstring[i]
    elif i % keyLengthEstimator == 2:
        cipherColumns[2] += cipherstring[i]
    elif i % keyLengthEstimator == 3:
        cipherColumns[3] += cipherstring[i]
    elif i % keyLengthEstimator == 4:
        cipherColumns[4] += cipherstring[i]

I have the feeling, that there is a more efficient way to do it. In Matlab there would be the reshape function, is there a similar function in Python?

Could you provide some example inputs and outputs?

mattsap
– mattsap

2016-05-24 19:01:49 +00:00
Commented May 24, 2016 at 19:01 — mattsap
– mattsap, Commented May 24, 2016 at 19:01

Kevin · Accepted Answer · 2016-05-24 19:04:11Z

2

You could slice the string N times, specifying a step of N for each one:

>>> s = "Hello I am the input string"
>>> columns = 5
>>> seq = [s[i::columns] for i in range(columns)]
>>> print seq
['H  i n', 'eItnsg', 'l hpt', 'laeur', 'om ti']
>>> print "\n".join(seq)
H  i n
eItnsg
l hpt
laeur
om ti

answered May 24, 2016 at 19:04

Kevin

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Comments

Jules · Accepted Answer · 2016-05-24 18:57:59Z

2

Why not simply:

#Divide the cipher text in the estimated number of columns
for i in range(0,keyLengthEstimator):
    cipherColumns.append(cipherstring[i])

for i in range(keyLengthEstimator,len(cipherstring)):
    cipherColumns[i % keyLengthEstimator] += cipherstring[i]

answered May 24, 2016 at 18:57

Jules

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1 Comment

smonsays Over a year ago

Thank you! That's much more elegant!

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