# OEFPHistogram¶

```
class OEFPHistogram
```

The `OEFPHistogram` class is used to hold a histogram
of similarity scores.

This class is an efficient way to obtain statistics on large databases which would be unfeasible to keep as full NxN similarity matrices.

- The following classes derive from this class:

See also

## Constructors¶

```
OEFPHistogram(size_t numBins=200, double min=0.0, double max=1.0)
```

Creates an `OEFPHistogram` object with given number of
bins and range.

**nrbins**- Number of bins in the histogram. (default=200)
**min**- Minimum bound (inclusive) of the histogram range. (default = 0)
**max**- Maximum bound (inclusive) of the histogram range. (default = 1)

Note

The default range of [0,1] covers all built-in similarity measures.

## AddSample¶

```
size_t AddSample(const float sample)
```

Adds the sample into the histogram by incrementing the count in the relevant bin. Returns the bin index that the sample went into.

## GetBinBoundaries¶

```
OESystem::OEIterBase<double> *GetBinBoundaries() const
```

Returns an iterator over the boundaries for each bin.

Note

The number of elements in this iterator is equal to
`OEFPHistogram::NumBins` **+1**.

## GetBinCenters¶

```
OESystem::OEIterBase<double> *GetBinCenters() const
```

Returns an iterator over the center value for each bin.

Note

The number of elements in this iterator is equal to
`OEFPHistogram::NumBins`.

Hint

It is generally reasonable to plot the results of
`OEFPHistogram::GetCounts` or
`OEFPHistogram::GetDensity` against the bin centers
returned by this method.

## GetBinIdx¶

```
size_t GetBinIdx(const float sample) const
```

Returns the bin index that the sample would go into without actually adding the sample into the bin.

## GetCounts¶

```
OESystem::OEIterBase<unsigned int> *GetCounts() const
```

Returns an iterator over the bin counts.

Note

Even though counts are returned as unsigned integers, they are internally
kept as size_t. If the counts are overflowing the unsigned int type of
the system, it may be more appropriate to use the normalized
`OEFPHistogram::GetDensity` instead.

## GetDensity¶

```
OESystem::OEIterBase<double> *GetDensity() const
```

Returns an iterator over the probability density for each bin.

Note

Result is equivalent to `OEFPHistogram::GetCounts`
normalized by `OEFPHistogram::NumSamples`.

## Mean¶

```
double Mean()
```

Approximates and returns the sample mean over the histogram.

Note

This approximation is affected by number of bins in the histogram.

## Std¶

```
double Std()
```

Approximates and returns the sample standard deviation over the histogram.

Note

This approximation is affected by number of bins in the histogram.