Algorithm to measure similarity between two sequences of strings

Question

How can I measure similarity-percentage between two sequences of strings?

I have two text files and In files there sequences are written like

First file:

AAA BBB DDD CCC GGG MMM AAA MMM

Second file:

BBB DDD CCC MMM AAA MMM

How to measure similarity between these two files in terms of order of strings?

For example in above example both files have similarity due to order of strings is same however some strings are missing in file-2. What algorithm is best suitable to solve this problem so that I can measure how similar is order of strings not frequency of strings in two?

alexn · Accepted Answer · 2012-06-01 05:58:00Z

You could use the Levenstein Distance algorithm. It analyzes how many edits that is needed to transform one string into another. This article explains it pretty well, and a sample implementation is provided.

Copy paste from Codeproject:

1.  Set n to be the length of s. ("GUMBO")
    Set m to be the length of t. ("GAMBOL")
    If n = 0, return m and exit.
    If m = 0, return n and exit.
    Construct two vectors, v0[m+1] and v1[m+1], containing 0..m elements.
2.  Initialize v0 to 0..m.
3.  Examine each character of s (i from 1 to n).
4.  Examine each character of t (j from 1 to m).
5.  If s[i] equals t[j], the cost is 0.
    If s[i] is not equal to t[j], the cost is 1.
6.  Set cell v1[j] equal to the minimum of:
    a. The cell immediately above plus 1: v1[j-1] + 1.
    b. The cell immediately to the left plus 1: v0[j] + 1.
    c. The cell diagonally above and to the left plus the cost: v0[j-1] + cost.
7.  After the iteration steps (3, 4, 5, 6) are complete, the distance is found in the cell v1[m].

Brent Worden · Accepted Answer · 2016-06-16 02:32:25Z

6

You can use python's SequenceMatcher.ratio function which measures the sequences similarity as a float in the range [0, 1]. If T is the total number of elements in both sequences, and M is the number of matches, this is 2.0 * M / T. The main code is as follows:

from difflib import SequenceMatcher
text1 = 'AAA BBB DDD CCC GGG MMM AAA MMM'
text2 = 'BBB DDD CCC MMM AAA MMM'
s = SequenceMatcher(None, text1, text2)
similarity = s.ratio() * 100

I hope this could help you!

edited Jun 16, 2016 at 2:32

Brent Worden

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answered Feb 19, 2015 at 8:00

AubreHarmon

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1 Comment

Fatima Over a year ago

the number 2.0 is referred to what?

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