grpstats (Statistics Toolbox)

Summary statistics by group.

Syntax

means = grpstats(X,group)
[means,sem,counts] = grpstats(X,group)
grpstats(x,group)
grpstats(x,group,alpha)

Description

means = grpstats(X,group) returns the means of each column of X by group. X is a matrix of observations. group is a column of positive integers that indicates the group membership of each row in X.

[means,sem,counts] = grpstats(x,group,alpha) supplies the standard error of the mean in sem. counts is the same size as the other outputs. The i-th row of counts contains the number of elements in the i-th group.

grpstats(x,group) displays a plot of the means versus index with 95% confidence intervals about the mean value of for each value of index.

grpstats(x,group,alpha) plots 100(1 - alpha)% confidence intervals around each mean.

Example

We assign 100 observations to one of four groups. For each observation we measure five quantities with true means from 1 to 5. grpstats allows us to compute the means for each group.

group = unidrnd(4,100,1);
true_mean = 1:5;
true_mean = true_mean(ones(100,1),:);
x = normrnd(true_mean,1);
means = grpstats(x,group)

means =

    0.7947    2.0908    2.8969    3.6749    4.6555
    0.9377    1.7600    3.0285    3.9484    4.8169
    1.0549    2.0255    2.8793    4.0799    5.3740
    0.7107    1.9264    2.8232    3.8815    4.9689