scalanlp/breeze

SparseArray/SparseVector.compact should be split into 2-3 functions

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#422 opened on Jul 23, 2015

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Description

Currently, SparseArray/SparseVector.compact does two separate things which are usually not intended to be done together. It should be split into three functions:

1: Add a def filter(predicate: T => Boolean): Unit function that allows specifying a predicate which is then used to strip certain values from the array/vector without reallocation.

2: Add a function called def tailor(): Unit that cuts down the memory usage to whatever is required to hold the values.

3: For backwards compatibility, replace the function compact with a function that calls filter(x => x == zero.zero) and then tailor().

Contributor guide

Tech stack
scala
Domain
dataperformance
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Scala knowledgeFamiliarity with sparse data structures
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
Examine the current implementation of SparseArray.compact and SparseVector.compact in the breeze source code (likely under breeze/src/main/scala/breeze/linalg/). Understand how it combines filtering zeros and memory tailoring. Implement a new filter(predicate) method, a tailor() method, and redefine compact to call both. Ensure backward compatibility. Look at existing tests for guidance.