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80 lines
3.6 KiB
Markdown
80 lines
3.6 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/RunningMedian/blob/master/LICENSE)
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[](https://github.com/RobTillaart/RunningMedian/releases)
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# RunningMedian
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Arduino library to determine the running median by means of a circular buffer.
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## Description
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Running Median looks like a running average with a small but important twist.
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Running average averages the last N samples while the running median takes
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the last N samples, sort them and take the middle one, or the average of the
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middle two in case the internal buffer size is even.
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Important differences between running average and running median:
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- Running median will return real data (e.g. a real sample from a sensor)
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if one uses an odd size of the buffer (therefor preferred).
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Running average may return a value that is never sampled.
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- Running median will give zero weight to outliers, and 100% to the middle sample,
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whereas running average gives the same weight to all samples.
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- Running median will give often constant values for some time.
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- As one knows the values in the buffer one can predict the maximum change of
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the running median in the next steps in advance.
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- Running median is slower as one needs to keep the values in timed order
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to remove the oldest and keep them sorted to be able to select the median.
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#### Note MEDIAN_MAX_SIZE
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The maximum size of the internal buffer is defined by **MEDIAN_MAX_SIZE** and is
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set to 255 (since version 0.3.1). The memory allocated currently is in the order
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of 5 bytes per element plus some overhead, so 255 elements take ~1300 bytes.
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For an UNO this is quite a bit.
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With larger sizes the performance penalty to keep the internal array sorted
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is large. For most applications a value much lower e.g. 19 is working well, and
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is performance wise O(100x) faster in sorting than 255 elements.
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## Interface
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### Constructor
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- **RunningMedian(const uint8_t size)** Constructor, dynamically allocates memory.
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- **~RunningMedian()** Destructor
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- **uint8_t getSize()** returns size of internal array
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- **uint8_t getCount()** returns current used elements, getCount() <= getSize()
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- **bool isFull()** returns true if the internal buffer is 100% filled.
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### Base functions
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- **clear()** resets internal buffer and variables, effectively emptird thr buffer.
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- **add(const float value) ** adds a new value to internal buffer, optionally replacing the oldest element if the buffer is full
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- **float getMedian()** returns the median == middle element
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- **float getAverage()** returns average of **all** the values in the internal buffer
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- **float getAverage(uint8_t nMedian)** returns average of **the middle n** values.
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This effectively removes noise from the outliers in the samples.
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- **float getHighest()** get the largest values in the buffer.
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- **float getLowest()** get the smallest value in the buffer.
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- **float getQuantile(const float q)** returns the Quantile value from the buffer.
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This value is often interpolated.
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### Less used functions
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- **float getElement(const uint8_t n)** returns the n'th element from the values in time order.
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- **float getSortedElement(const uint8_t n)** returns the n'th element from the values in size order (sorted ascending)
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- **float predict(const uint8_t n)** predict the max change of median after n additions, n should be smaller than **getSize()/2**
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## Operation
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See examples
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