Search replace patterns in a Python list

Question

I have a list of Rubik's Cube movements and a dictionary of shortcuts like this :

mvts = ['U', 'U', 'R', 'Ri', 'L2', ...]
shortcuts = {'UU' : 'U2', 'RRi' : '', ...}

What I'm trying to do is applying a "search and replace" on the mvts list based on the contents of shortcuts.

Here is what the result would be in the example :

mvts = ['U2', 'L2', ...]

I'm using Python3 and I can't use a library that doesn't come with Python from scratch.

I'm stuck. I can do this with some regex on a String but I don't see how to make this search quick on my list.

ᴀʀᴍᴀɴ · Accepted Answer · 2016-01-09 21:04:06Z

1

Try this :

for i in range(len(mvts)):
      if(mvts[i] in shortcuts):
           mvts[i] = shortcuts[mvts[i]]

Notice

If you are Already sure that list elements exist in dictionary you can delete if line

and if you want delete duplications in list:

mvts = list(set(mvts))

answered Jan 9, 2016 at 21:04

ᴀʀᴍᴀɴ

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1 Comment

Guillaume Wuip Over a year ago

Thanks @arman. Your code doesn't really do what I need as mvts[i] - which is a single mouvement - is not in shortcuts. But maybe mvts[i]+mvts[i+1] is, for example.

Martin Konecny · Accepted Answer · 2016-01-09 21:38:22Z

0

You could use re.sub

import re

mvts = ['UUU', 'U', 'R', 'Ri', 'L2']
shortcuts = {'UU' : 'U2', 'RRi' : ''}

def do_sub(m):
    for k, v in shortcuts.items():
        m = re.sub(k, v, m)
    return m

[do_sub(m) for m in mvts]

Output:

['U2U', 'U', 'R', 'Ri', 'L2']

edited Jan 9, 2016 at 21:38

answered Jan 9, 2016 at 21:02

Martin Konecny

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2 Comments

Guillaume Wuip Over a year ago

Thank you @martin-konecny but I don't have directly 'UUU' in mvts so I can't use re on each list cell. I have instead ['U', 'U', 'U', ...]. I'm going to look for a way to group successive same cells.

Guillaume Wuip Over a year ago

Ok so I've found a way to group ['U', U', ...] into ['UU'] with itertools.groupbyand then using re on that. But I'm not grouping ['Ri', 'R', ...] for example.

Community · Accepted Answer · 2017-05-23 11:59:15Z

0

I've found a solution by googling with the good terms : "Search/replace sublist in list Python".

So I've used @latty's solution explained here https://stackoverflow.com/a/12898180/2058840.

I had to change my dictionary structure to :

shortcuts = {'U U' : ['U2'], 'R Ri' : '', ...}

And then :

for (sublist, shortcut) in shortcuts:
    replace_list(mvts, sublist.split(), shortcut) #@latty's function

Thanks @martin-konecny and @arman for your help !

edited May 23, 2017 at 11:59

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answered Jan 10, 2016 at 8:16

Guillaume Wuip

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