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117 lines
4.3 KiB
Markdown
117 lines
4.3 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/SparseArray/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/SparseArray/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/SparseArray/blob/master/LICENSE)
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[](https://github.com/RobTillaart/SparseArray/releases)
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# SparseArray
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Arduino library for sparse arrays of floats.
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TODO REDO DOCUMENTATION.
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## Description
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SparseArray is an **experimental** library to implement a one
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dimensional sparse array of floats (a.k.a. vector) on an Arduino.
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A sparse array is a mn array with mostly zeros and a low percentage
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non-zero values.
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The purpose of this library is efficient storage in memory.
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The maximum array that can be represented is 65535 elements
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with a theoretical maximum of 65535 non-zero elements.
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(although that does not make sense due to overhead)
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In practice the library limits this to 1000 non-zero elements.
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Note: 255 elements would still fit in an UNO's 2K memory.
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Relates to:
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- https://github.com/RobTillaart/SparseMatrix
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- https://github.com/RobTillaart/distanceTable
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Note: this library is derived from SparseMatrix.
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#### Implementation
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The implementation is based on 2 arrays holding ``` x, value```
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where value is float, and x is an uint16_t.
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That are 6 bytes per element.
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The number of elements that the sparse array object can hold are
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given as parameter to the constructor.
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If the space cannot be allocated the size is set to zero.
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In the future other data types should be possible.
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#### Performance
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The elements are not kept sorted or indexed so optimizations might be
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possible but are not investigated yet.
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There is however a test sketch to monitor the performance of
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the most important functions.
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Accessing elements internally is done with a linear search,
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which becomes (much) slower if the number of elements is increasing.
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This means that although in theory there can be 65535 elements,
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in practice a few 100 can already become annoyingly slow.
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To keep performance a bit the library has a limit build in.
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Check the .h file for **SPARSEARRAY_MAX_SIZE 1000**
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## Interface
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```cpp
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#include "SparseArray.h"
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```
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### Constructor + meta
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- **SparseArray(uint16_t size)** constructor.
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Parameter is the maximum number of elements in the sparse array.
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Note this number is limited to **SPARSEARRAY_MAX_SIZE 1000**.
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If the space requested cannot be allocated size will be set to 0.
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- **uint16_t size()** maximum number of elements.
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If this is zero, a problem occurred with allocation happened.
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- **uint16_t count()** current number of elements in the array.
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Should be between 0 and size.
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- **float sum()** sum of all elements ( != 0 ) in the array.
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- **void clear()** resets the array to all zero's again.
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### Access
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- **bool set(uint16_t x, float value)** gives an element in the array a value.
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If the value is set to zero, it is removed from the internal store.
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Returns false if the internal store is full, true otherwise.
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- **float get(uint16_t x)** returns a value from the array.
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- **bool add(uint16_t x, float value)** adds value to an element in the array.
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If needed a new internal element is created.
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If the sum is zero, the element is removed from the internal store.
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Returns false if the internal store is full, true otherwise.
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- **void boundingSegment(uint16_t &minX, uint16_t &maxX)**
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Returns the bounding box in which all values != 0 are located.
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This can be useful for printing or processing the non zero elements.
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## Future
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- documentation
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- test
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- keep in sync with SparseMatrix where possible
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- merge into one class hierarchy?
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- dump should be in the class?
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- or as static function...
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- stream as param dump(Stream str, ...
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#### ideas
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- array { uint32_t, float }; for logging millis/micros + measurement
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delta coding of time stamp? if it fit in 16 bit?
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=> sounds like a class on its own.
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