Popular recipes tagged "partition" but not "splitting"

Generate the partitions of a set, by index (Python)

2010-04-30T11:07:30-07:00

Python recipe 577211 by Anton Vredegoor (combinatorics, partition).

Sets of only a few items already have many ways they can be partitioned into subsets. Therefore it can be useful to generate these partitions by index, like the partition class were some large list where one can just access element "i". Of course one should not compute the whole list in advance but compute the partitions on the fly. This recipe was originally extracted form a book by Kreher and Stinson. Over the years I came back to my code from time to time creating a new and hopefully more pythonic version each time I understood it better. My current take on it is that the algorithm looks a lot like creating a Pascals triangle in order to compute combinations. One just tries to find a way down the triangle to a specific element, each time subtracting the amounts the different positions in the triangle account for. It is also similar to finding indexed permutations of a set with elements occurring more than once. One of these days I will perhaps understand how all of this fits together. Until then I'll post code solving specific situations.

string multi-partitioning (Python)

2010-03-26T20:03:59-07:00

Python recipe 577017 by Michael Grünewald (partition, string). Revision 6.

Works like the partition method of strings in Python2.5+, but has support for more than one delimiter.

Better description by Gabriel Genellina:

Split the string at separator boundaries. The separators are searched from left to right, in the same order specified, and one after another. Unlike partition, all of them must be present (else ValueError is raised). Only one split per separator occurrence is done. Returns a list containing one more element than separators were given: first, text from beginning of the string up to (but not including) the first separator; the first separator itself; text between the first separator and the second one; the second separator; and so on. The last element contains all text following the last separator.

Partition an iterable into n lists (Python)

2009-05-30T16:35:27-07:00

Python recipe 576785 by Ian Eloff (iterator, partition).

This could also be easily modified to return n iterators, but was outside of my needs. Handy for splitting up the workload for use with multiple threads/processes.