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Function Reference: grpstats

statistics: mean = grpstats (x)
statistics: mean = grpstats (x, group)
statistics: [a, b, …] = grpstats (x, group, whichstats)
statistics: [a, b, …] = grpstats (x, group, whichstats, alpha)

Summary statistics by group. grpstats computes groupwise summary statistics, for data in a matrix x. grpstats treats NaNs as missing values, and removes them.

means = grpstats (x, group), when X is a matrix of observations, returns the means of each column of x by group. group is a grouping variable defined as a categorical variable, numeric, string array, or cell array of strings. group can be [] or omitted to compute the mean of the entire sample without grouping.

[a, b, …] = grpstats (x, group, whichstats), for a numeric matrix X, returns the statistics specified by whichstats, as separate arrays a, b, …. whichstats can be a single function name, or a cell array containing multiple function names. The number of output arguments must match the number of function names in whichstats. Names in whichstats can be chosen from among the following:

"mean"mean
"median"median
"sem"standard error of the mean
"std"standard deviation
"var"variance
"min"minimum value
"max"maximum value
"range"maximum - minimum
"numel"count, or number of elements
"meanci"95% confidence interval for the mean
"predci"95% prediction interval for a new observation
"gname"group name

[…] = grpstats (x, group, whichstats, alpha) specifies the confidence level as 100(1-ALPHA)% for the "meanci" and "predci" options. Default value for alpha is 0.05.

Examples:

 
 load carsmall;
 [m,p,g] = grpstats (Weight, Model_Year, {"mean", "predci", "gname"})
 n = length(m);
 errorbar((1:n)',m,p(:,2)-m)
 set (gca, "xtick", 1:n, "xticklabel", g);
 title ("95% prediction intervals for mean weight by year")

See also: grp2idx

Source Code: grpstats

Example: 1

  

 load carsmall;
 [m,p,g] = grpstats (Weight, Model_Year, {"mean", "predci", "gname"})
 n = length(m);
 errorbar((1:n)',m,p(:,2)-m);
 set (gca, "xtick", 1:n, "xticklabel", g);
 title ("95% prediction intervals for mean weight by year");

m =

   3441.3
   3078.7
   2453.5

p =

   1847.1   5035.6
   1457.0   4700.4
   1754.1   3153.0

g =
{
  [1,1] = 70
  [2,1] = 76
  [3,1] = 82
}
plotted figure

Example: 2

  

 load carsmall;
 [m,p,g] = grpstats ([Acceleration,Weight/1000],Cylinders, ...
                     {"mean", "meanci", "gname"}, 0.05)
 [c,r] = size (m);
 errorbar((1:c)'.*ones(c,r),m,p(:,[(1:r)])-m);
 set (gca, "xtick", 1:c, "xticklabel", g);
 title ("95% prediction intervals for mean weight by year");

m =

   11.6406    3.9703
   16.6706    2.3726
   16.4765    3.1255

p =

   11.1762    3.8899   12.1050    4.0506
   16.1385    2.2998   17.2027    2.4454
   16.1622    3.0518   16.7907    3.1992

g =
{
  [1,1] = 8
  [2,1] = 4
  [3,1] = 6
}
plotted figure