## DESCRIPTION

r3.univar calculates the univariate statistics for a 3D raster map. This includes the number of cells counted, minimum and maximum cell values, range, arithmetic mean, population variance, standard deviation, coefficient of variation, and sum. Statistics are calculated separately for every category/zone found in the zones input map if given. If the -e extended statistics flag is given the 1st quartile, median, 3rd quartile, and given percentile are calculated. If the -g flag is given the results are presented in a format suitable for use in a shell script. If the -t flag is given the results are presented in tabular format with the given field separator. The table can immediately be converted to a vector attribute table which can then be linked to a vector, e.g. the vector that was rasterized to create the zones input raster.

## NOTES

As with most GRASS raster3d modules, r3.univar operates on the voxel array defined by the current 3d region settings, not the original extent and resolution of the input map. See g.region.

This module can use large amounts of system memory when the -e extended statistics flag is used with a very large region setting. If the region is too large the module should exit gracefully with a memory allocation error. Basic statistics can be calculated using any size input region.

## EXAMPLE

Computing univariate statistics of a 3D raster with randomly generated values:

    # define volume
    g.region n=10 s=0 w=0 e=10 b=0 t=10 res=1 res3=1 -p3

    # generate random map
    r3.mapcalc "random_0_1 = rand(0., 1)" -s

    # compute univariate statistics, along with extended statistics
    r3.univar -e map=random_0_1 percentile=98
     100%
    total null and non-null cells: 1000
    total null cells: 0

    Of the non-null cells:
    ----------------------
    n: 1000
    minimum: 0.00053905
    maximum: 0.998322
    range: 0.997783
    mean: 0.513676
    mean of absolute values: 0.513676
    standard deviation: 0.289969
    variance: 0.0840821
    variation coefficient: 56.4498 %
    sum: 513.676463040334
    1st quartile: 0.257654
    median (even number of cells): 0.524313
    3rd quartile: 0.763637
    98th percentile: 0.982924

    # script style output, along with extended statistics
    r3.univar -ge map=random_0_1 percentile=98
    n=1000
    null_cells=0
    cells=1000
    min=0.000539049520323687
    max=0.998322037540536
    range=0.997782988020212
    mean=0.513676463040334
    mean_of_abs=0.513676463040334
    stddev=0.289969154194666
    variance=0.0840821103843701
    coeff_var=56.4497646005434
    sum=513.676463040334
    first_quartile=0.257654
    median=0.524313
    third_quartile=0.763637
    percentile_98=0.982924

## TODO

To be implemented mode, skewness, kurtosis.

## SEE ALSO

g.region, r.univar, r.mode, r.quantile, r.series, r3.stats, r.statistics, v.rast.stats, v.univar

## AUTHORS

Soeren Gebbert
Code is based on r.univar from
Hamish Bowman, Otago University, New Zealand
and Martin Landa
Zonal loop by Markus Metz

Last changed: $Date$