Python: rearranging an array of strings

Question

I'm trying to rearrange the following array of strings:

myString =['000', ['1', 'two', 'three'], ['1', 'b', 'c']]

So that myString2 looks like

myString2 = [['000', '1', 'two', 'three'], [['000', '1', 'b', 'c']]

Looking around for some ideas (e.g. here) I attempted the following loop:

myString2 = []
for i in range(0,len(myString)-1):
    myString2 [i].append(myString[0])
    myString2 [i].append(myString[i])

But I get an error which I don't really understand :

IndexError: list index out of range

I'm fairly new to python and wonder if there is perhaps a simpler way than my current idea, and if not, if someone could kindly explain what is preventing the loop from running.

Second nested expected should start with only a single bracket. — Mad Physicist
– Mad Physicist, Commented Mar 9, 2017 at 18:13
I think you need to give more details as to what you are trying to accomplish, and the sorts of inputs you are expecting. It's difficult to give some sort of general solution without you elaborating a bit. For example, do you expect to deal with something like ['000', ['1', 'two', 'three'], ['1', 'b', 'c'], '001'], and if so, what output do you expect? — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Mar 9, 2017 at 18:13
Also your "attempt" will get a NameError before anything else as posted. — Mad Physicist
– Mad Physicist, Commented Mar 9, 2017 at 18:14

hansaplast · Accepted Answer · 2017-03-09 19:42:38Z

2

You were close with your script, this works:

myString =['000', ['1', 'two', 'three'], ['1', 'b', 'c']]
myString2 = []
for i in range(1,len(myString)):
    myString2.append(myString[0])
    myString2.append(myString[i])

What was wrong?

myString2[i].append attempts to append something at myString, index i, so at first iteration it tries to access myString[0] but myString is still empty, that causes the out of range error. Instead use append just on the list and it will add the element at the last position
you need to loop from the second element range(1,...
range is exclusive, so a range(1,5) is [1,2,3,4] -> you don't need to substract 1

answered Mar 9, 2017 at 19:42

hansaplast

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2 Comments

Jean-François Fabre Over a year ago

upvote for taking the time to understand the OP code issue :)

sc28 Over a year ago

Yes thanks, this is very helpful! So now I know a new way for a clean one-liner, and also understand the logic of my heavier code :)

Jean-François Fabre · Accepted Answer · 2017-03-09 18:14:29Z

1

The snippet of code you provided cannot work because of variable names, so I won't try to explain you what's wrong with it further.

That said, those problems can be easily done in one-liners using list comprehensions:

myString =['000', ['1', 'two', 'three'], ['1', 'b', 'c']]

new_string = [[myString[0]]+s for s in myString[1:]]

print(new_string)

just create a new list of lists, with the first element as head, and the rest as tail.

Results as:

[['000', '1', 'two', 'three'], ['000', '1', 'b', 'c']]

answered Mar 9, 2017 at 18:14

Jean-François Fabre♦

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1 Comment

sc28 Over a year ago

Great one liner! Thanks for seeing through the typos in the variables, this was exactly what I was hoping for.

Chris · Accepted Answer · 2017-03-09 18:20:19Z

0

Instead of trying to use the first list to hold the string 0000, why not put it in a constant instead

MAGIC_STRING = '0000'

and then simply use the constant to create the new, modified sublists:

myString = [['1', 'two', 'three'], ['1', 'b', 'c']]
myString2 = [[MAGIC_STRING] + el for el in myString]

answered Mar 9, 2017 at 18:20

Chris

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