Variation of suffix array in python

Question

I'm relatively new to computer science, and I'm learning how to code in python. I'm trying to figure out how to make a function that takes a list and returns a list of suffixes from the inputted list, in order from shortest length to longest length. For example, entering [3,4,2,-9,7,6,1] to the function would return [[],[1],[6,1],[7,6,1],[-9,7,6,1],[2,-9,7,6,1],[4,2,-9,7,6,1],[3,4,2,-9,7,6,1]]

I've tried several approaches, but so far I'm not having much luck. Here is what I have so far:

def h(m):
    newlist = []
    x = 0
    y = (len[m])-1
    while x in range(y):
        sublist = []
        sublist = sublist + m[x:y]
        newlist.append(sublist)
        x += 1
    return new list

When I try to run the function by entering something like

a = [3,4,2,-9,7,6,1]
h(a)

I get an error:

Traceback (most recent call last):
File "<pyshell#239>", line 1, in <module>
h(a)
File "<pyshell#238>", line 4, in h
y = (len[m])-1
TypeError: 'builtin_function_or_method' object has no attribute '__getitem__'

My objective with this bit of code was simply to create a the list of suffixes without sorting them by length. After I figure out how to create this new list I will add the sorting bit of the code. Keep in mind this is not a homework assignment. Any help would be greatly appreciated!

mpolednik · Accepted Answer · 2015-05-03 23:43:46Z

3

Possible solution is using list comprehension:

[l[i:] for i in range(len(l), -1, -1)]

This code uses slicing and list comprehension to simply return a list of slices from the end. Using your code, small modification is required - len is a function and not a dictionary, therefore you need to use the call operator () instead of subscript operator [].

y = len(m) - 1

That will not yield correct result though, because you will not get the last suffix and empty suffix. In order to cover these two, you will need to modify y or the loop to cover them

y = len(m) + 1

or better

while x in range(y + 1):

edited May 3, 2015 at 23:43

answered May 3, 2015 at 23:21

mpolednik

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2 Comments

mpolednik Over a year ago

It is because range isn't inclusive from the right: range(5) actually returns [0, 1, 2, 3, 4]. So, you wouldn't do a [7:7] but [6:7]. It would be nicer to handle this case in the loop itself - making it range(y + 1).

Nick Borisenko Over a year ago

sorry I just deleted my comment because I figured out what it's doing. Thank you so much!

Haochen Wu · Accepted Answer · 2015-05-03 23:21:11Z

0

use parenthesis to get the length of the list:

y = len(m) - 1

answered May 3, 2015 at 23:21

Haochen Wu

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1 Comment

Haochen Wu Over a year ago

You probably should use mpolednik's answer anyway. It's more pythonic.

Zizouz212 · Accepted Answer · 2015-05-03 23:22:57Z

0

Your error is in your len:

(len[m]) - 1

len is a function, and you can't index or slice or the what not. Do this instead:

y = len(m) - 1

There's also one other error:

return new list

Should be: (You can't have spaces in variables)

return newlist

answered May 3, 2015 at 23:22

Zizouz212

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