SEP 2016: histplot() and histc() upgrade
A bit of history
- to split the computation of an histogram on one hand, and its display on the other hand.
- to become able to get the histogram's data that -- up to then -- were not available from histplot()
- to introduce a "normalized" way to compute the histogram heights.
It introduced in Scilab 5.4 a new histc() macro having the same syntaxes as histplot() for input data, and returning histogram's heights and memberships of input data in defined bins. See https://codereview.scilab.org/#/c/13155/: new histc() + histplot() output added.
The normalization option has been badly designed, since several ways to normalize data can be defined, whereas a boolean can take only one active value.
By the way, these ways to compute the histogram do not normalize heights or area, in such a way that the name of this option is misleading. It shall be changed.
normalization has been appended to the very long list of input parameters, instead of being inserted after data -- as for histc() -- and before graphical options.
the default normalization value has been set to %T and then breaks back-compatibility for nothing.
By chance, neither the normalization nor the polygon options implemented for histplot() were yet documented for it in Scilab 5.5.2.
Moreover, other features are still missing:
- Only one method to compute bins is available. Other methods could be implemented and called through their name as a string.
- A default method to compute bins is missing.
Neither histc() nor histplot() return bin's edges when these ones are computed.
With histc(), it is now possible to compute an histogram out of histplot(), but there is still no way to make histplot() just plotting it without recomputing it.
As for the normalization option, the histplot() polygon option has been appended to the list of input parameters instead of being inserted before the style option.
- Only vertical-up histograms can be displayed. vertical-down and Horizontal histograms shall become available.
- Polar histograms shall be supported.
- There is no option to display heights values on the bars.
Processing of -%inf, %inf, and %nan values is undefined. There should be ways to make then counted and become able to ignore them or to take them into account when required.
histc() and histplot() do not yet support text data, despite dsearch() on witch histc() is based was extended to text since Scilab 5.5.0.
New syntaxes proposed
[ heights ] = ..
[heights, memberships] = ..
.. = histc(nBins, data)
.. = histc(edges, data)
histc(.., data, normalization)
If backward-compatibility is of concern despite the short history of the normalization option, this one may be warn-obsoleted (for some while or forever) and automatically translated using the histScale option.
histc(binsMethod, data) with binsMethod = "sqrt"(default) | "sturges" | "freediac":
sqrt: nbins = sqrt(size(data,"*")
sturges: Sturges criteria: nbins = ceil(1 + log2(size(data,"*")))
freediac: Freedman-Diaconis criteria: binWidth = 2*iqr(data)*size(data,"*")^(-1/3). This method can't be applied to text data.
histc(.., data, histScale) with histScale = "counts"|"countsNorm"|"density"|"densityNorm":
"counts": the height is the bin's number of members (default)
"density": the bin's area is the bin's number of members
"countsNorm": as "counts", divided by the total number of data. Discussion: should -%inf, %inf, %nan values, or/and data out of defined bins be taken into account for the "normalization"?
"densityNorm": as "density", divided...
[heights, memberships, binsDef, outside] = histc(..) with
binsDef edges (continuous) or values (discrete)
outside = [Nminf, Npinf, Nnan] counts occurrences of -%inf, %inf and %nan values. In the membership array, -%inf will have the index -%inf, %inf will have the index %inf, and %nan will have the index -1
[heights, memberships] = histplot(Nbins|edges, data [, <graphical options>..])
[heights, memberships, binsDef, outside] = histplot(..) : as for histc(..) (see here-above)
histplot(.. data, histScale ..)
histplot(.. data, histScale, dispOptions ..) with dispOptions being a vector of one to five strings provided in any order, among the following, specifying options to display the histogram:
positions: "bottom" or "" (default) | "up" | "left" | "right" : draw the histogram with its base at the given position wrt its bars. Are these values clear enough?
"cumulate": draw the cumulated "staired" histogram instead of the simple one.
"polygon" : draw as well the polygon of frequencies or densities etc.
"polar" : draw the histogram in polar mode, bins being rescaled over the full [0, 180°] fan. Values of bins edges are displayed on an external graduated half circle.
"values" : display values of heights on the bars
histplot(binsType, bins, heights, dispOptions ..) to display as is an histogram already computed,
with binsType = "binsEdges" | "binsValues" : must be explicit (no default value)
Since allowed values of the binsType string are all distinct from values of the binsMethod string, parsing input arguments can easily detect this specific syntax.
Questions an discussion
Since now, since Scilab 5.4, histc() can compute and return histogram results, and that histplot() can be fed by them, should histplot() still return the results?
In output, do we shift the memberships array (introduced recently, 5.5.0) in 3rd position to put computed edges in argout#2?
How do we manage %nan and %inf ?
Author(s) : Samuel GOUGEON