Pattern detection in a string in Python

Question

I have a list of actions described with strings, ex "BPxPyPzPC" where each letter represents an action and C represents an event.

Some users' actions (such as "B", "Px", "Py" and "Pz") led to an event (in my example, the letter "C"), others did not, so I want to identify the pattern of actions (ex "BPxPyPz") that most often leads to the event, what is the most efficient way to do this in Python?

Thanks!

Example code:

c=['' for x in range(0,4)]
c[0]="BPxPxPyPC"
c[1]="BPxPyPyPC"
c[2]="BPyPxPyPC"
c[3]="BPyPxPyPC"

#do something

#desired result
The most likely sequence of actions to achieve "C" is "BPyPxPy"

fferri · Accepted Answer · 2018-05-02 13:22:18Z

3

It is not clear if and how do you want to discriminate the actions.

I used regular expressions to match any string followed by C, and Counter to get the most common string.

Here's the simplest thing to obtain your result:

import re
from collections import Counter

c = ["BPxPxPyPC", "BPxPyPyPC", "BPyPxPyPC", "BPyPxPyPC"]

cnt = Counter()
for sequence in c:
    m = re.match('^(.*)C$', sequence)
    if m: cnt.update([m.group(1)])

print('The most likely sequence is " {}"'.format(cnt.most_common(1)[0][0]))
# BPyPxPyP

edited May 2, 2018 at 13:22

answered May 2, 2018 at 13:14

fferri

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Comments

Mika72 · Accepted Answer · 2018-05-02 13:49:48Z

I would do something like this (takes into account only first sequence of actions that has max hits in stack for event ev):

def checkSeq(c, stack):
    stackSeqs = [x[0] for x in stack]

    if c not in stackSeqs:
        stack.append([c,0])
    else:
        idx = stackSeqs.index(c)
        stack[idx][1] += 1
    return stack

def max_act_ev(ev, stack):
    acts=[]
    for row in stack:
        if ev in row[0][-1]:
            acts.append(row)
    if len(acts) > 0:
        res = sorted(acts, key=lambda x: x[1],reverse=True)
        return res[0]
    else:
        return []


# Start of code

stack=[["BPyPxPyPC",1],["BPxPxPyPC",1],["BPxPxPxPC",1]]
c = "BPxPxPyPC"
ev = "C"

stack = checkSeq(c,stack)
seq = max_act_ev(ev,stack)

print(stack)
if len(seq)>0:
    print('The most likely sequence of actions to achieve "'+seq[0][-1]+'" is "'+seq[0][:-1]+'"')
else:
    print("No actions found for event "+ev)

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