ordinal

(Not Recommended) Arrays for ordinal data

The nominal and ordinal array data types are not recommended. To represent ordered and unordered discrete, nonnumeric data, use the Categorical Arrays data type instead.

Description

Ordinal data are discrete, nonnumeric values that have a natural ordering. ordinal array objects provide efficient storage and convenient manipulation of such data, while also maintaining meaningful labels for the values.

You can manipulate ordinal arrays like ordinary numeric arrays, by subscripting, concatenating, and reshaping. Use ordinal arrays as grouping variables when the elements indicate the group to which an observation belongs.

Creation

Syntax

B = ordinal(X)

B = ordinal(X,labels)

B = ordinal(X,labels,levels)

B = ordinal(X,labels,[],edges)

Description

B = ordinal(X) creates an ordinal array B from the array X. ordinal creates the levels of B from the sorted unique values in X, and creates default labels for the levels.

B = ordinal(X,labels) labels the levels in B according to labels.

B = ordinal(X,labels,levels) creates an ordinal array with possible levels defined by levels.

B = ordinal(X,labels,[],edges) creates an ordinal array by binning the numeric array X with bin edges given by the numeric vector edges.

Input Arguments

X — Input array

numeric | logical | character | string | categorical | cell array of character vectors

Input array to convert to ordinal, specified as a numeric, logical, character, string, or categorical array, or a cell array of character vectors. The levels of the resulting ordinal array correspond to the sorted unique values in X.

labels — Labels for discrete levels

character array | string array | cell array of character vectors

Labels for the discrete levels, specified as a character array, string array, or cell array of character vectors. By default, ordinal assigns labels to the levels in B in order of the sorted unique values in X.

You can include duplicate labels in labels to merge multiple values in X into a single level in B.

Data Types: char | string | cell

levels — Possible ordinal levels

vector

Possible ordinal levels for the output ordinal array, specified as a vector whose values can be compared to those in X using the equality operator. ordinal assigns labels to each level from the corresponding elements of labels. If X contains any values not present in levels, the levels of the corresponding elements of B are undefined.

edges — Bin edges

numeric vector

Bin edges used to create the ordinal array by binning a numeric array, specified as a numeric vector. The uppermost bin includes values equal to the rightmost edge. ordinal assigns labels to each level in the resulting ordinal array from the corresponding elements of labels. When you specify the edges input argument, it must have one more element than labels.

Output Arguments

B — Ordinal array

ordinal array object

Ordinal array, returned as an ordinal array object.

By default, an element of B is undefined if the corresponding element of X is NaN (when X is numeric), an empty character vector (when X is a character), an empty or missing string (when X is a string), or undefined (when X is categorical). ordinal treats such elements as undefined or missing and does not include entries for them among the possible levels. To create an explicit level for such elements instead of treating them as undefined, use the levels input argument and include NaN, the empty character vector, the empty or missing string, or an undefined element.

Object Functions

addlevels	(Not Recommended) Add levels to nominal or ordinal arrays
droplevels	(Not Recommended) Drop levels from a nominal or ordinal array
getlabels	(Not Recommended) Access nominal or ordinal array labels
getlevels	(Not Recommended) Access nominal or ordinal array levels
islevel	(Not Recommended) Determine if levels are in nominal or ordinal array
levelcounts	(Not Recommended) Element counts by level of a nominal or ordinal array
mergelevels	(Not Recommended) Merge levels of nominal or ordinal arrays
reorderlevels	(Not Recommended) Reorder levels of nominal or ordinal arrays
setlabels	(Not Recommended) Assign labels to levels of nominal or ordinal arrays

The following is a partial list of the many other MATLAB^® array functions you can use with ordinal arrays.

double	Double-precision arrays
histogram	Histogram plot
isequal	Determine array equality
isundefined	Find undefined elements in categorical array
pie	Legacy pie chart
summary	Data summary
times	Multiplication

Examples

Create and Label Ordinal Arrays

Create an ordinal array from integer data, providing explicit labels.

quality = ordinal([1 2 3 3 2 1 2 1 3],...
   {'low' 'medium' 'high'})

quality = 1x9 ordinal
     low      medium      high      high      medium      low      medium      low      high 

Show that the first element is less than the second element (low is less than medium).

quality(1) < quality(2)

ans = logical
   1

Create an ordinal array by binning values between 0 and 1 into thirds with labels 'small', 'medium', and 'large'.

X = rand(5,2)

X = 5×2

    0.8147    0.0975
    0.9058    0.2785
    0.1270    0.5469
    0.9134    0.9575
    0.6324    0.9649

A = ordinal(X,{'small' 'medium' 'large'},[],[0 1/3 2/3 1])

A = 5x2 ordinal
     large       small  
     large       small  
     small       medium 
     large       large  
     medium      large  

Create and Manipulate Ordinal Arrays

Create an ordinal array from integer data.

quality = ordinal([1 2 3; 3 2 1; 2 1 3],{'low' 'medium' 'high'})

quality = 3x3 ordinal
     low         medium      high 
     high        medium      low  
     medium      low         high 

Identify the elements in quality that are members of a level greater than or equal to 'medium'. A value of 1 in the resulting array indicates that the corresponding element of quality is a member of this level.

quality >= 'medium'

ans = 3x3 logical array

   0   1   1
   1   1   0
   1   0   1

Identify the elements in quality that are members of either the level 'low' or 'high'.

ismember(quality,{'low' 'high'})

ans = 3x3 logical array

   1   0   1
   1   0   1
   0   1   1

Merge the elements of the 'medium' and 'high' levels into a new level labeled 'ok'.

quality = mergelevels(quality,{'medium','high'},'ok')

quality = 3x3 ordinal
     low      ok       ok  
     ok       ok       low 
     ok       low      ok  

Display the levels of quality.

getlevels(quality)

ans = 1x2 ordinal
     low      ok 

Summarize the number of elements in each level. By default, summary returns counts for each column of the input array.

summary(quality)

     low      1      1      1 
     ok       2      2      2 

Version History

Introduced in R2007a