Learn more about Statistics Toolbox

Data with Missing Values

Many data sets have one or more missing values. It is convenient to code missing values as NaN (Not a Number) to preserve the structure of data sets across multiple variables and observations.

For example:

X = magic(3);
X([1 5]) = [NaN NaN]
X =
   NaN    1    6
     3  NaN    7
     4    9    2

Normal MATLAB arithmetic operations yield NaN values when operands are NaN:

s1 = sum(X)
s1 =
   NaN   NaN   15

Removing the NaN values would destroy the matrix structure. Removing the rows containing the NaN values would discard data. Statistics Toolbox functions in the following table remove NaN values only for the purposes of computation.

Function	Description
nancov	Covariance matrix, ignoring NaN values
nanmax	Maximum, ignoring NaN values
nanmean	Mean, ignoring NaN values
nanmedian	Median, ignoring NaN values
nanmin	Minimum, ignoring NaN values
nanstd	Standard deviation, ignoring NaN values
nansum	Sum, ignoring NaN values
nanvar	Variance, ignoring NaN values

For example:

s2 = nansum(X)
s2 =
     7    10    15

Other Statistics Toolbox functions also ignore NaN values. These include iqr, kurtosis, mad, prctile, range, skewness, and trimmean.

Resampling Statistics

Statistical Visualization

© 1984-2009- The MathWorks, Inc.    -   Site Help   -   Patents   -   Trademarks   -   Privacy Policy   -   Preventing Piracy   -   RSS