# r.univar.1grass man page

**r.univar** — Calculates univariate statistics from the non-null cells of a raster map.

Statistics include number of cells counted, minimum and maximum cell values, range, arithmetic mean, population variance, standard deviation, coefficient of variation, and sum.

## Keywords

raster, statistics, univariate statistics, zonal statistics

## Synopsis

**r.univar****r.univar --help****r.univar** [-**get**] **map**=*name*[,*name*,...] [**zones**=*name*] [**output**=*name*] [**percentile**=*float*[,*float*,...]] [**separator**=*character*] [**--overwrite**] [**--help**] [**--verbose**] [**--quiet**] [**--ui**]

### Flags

**-g**- Print the stats in shell script style
**-e**- Calculate extended statistics
**-t**- Table output format instead of standard output format
**--overwrite**- Allow output files to overwrite existing files
**--help**- Print usage summary
**--verbose**- Verbose module output
**--quiet**- Quiet module output
**--ui**- Force launching GUI dialog

### Parameters

**map**=*name[,name*,...]**[required]**- Name of raster map(s)
**zones**=*name*- Raster map used for zoning, must be of type CELL
**output**=*name*- Name for output file (if omitted or "-" output to stdout)
**percentile**=*float[,float*,...]- Percentile to calculate (requires extended statistics flag)

Options:*0-100*

Default:*90* **separator**=*character*- Field separator

Special characters: pipe, comma, space, tab, newline

Default:*pipe*

## Description

*r.univar* calculates the univariate statistics of one or several raster map(s). 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.

When multiple input maps are given to *r.univar*, the overall statistics are calculated. This is useful for a time series of the same variable, as well as for the case of a segmented/tiled dataset. Allowing multiple raster maps to be specified saves the user from using a temporary raster map for the result of *r.series* or *r.patch*.

## Notes

As with most GRASS raster modules, *r.univar* operates on the raster array defined by the current 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.

Without a **zones** input raster, the *r.quantile* module will be significantly more efficient for calculating percentiles with large maps.

For calculating univariate statistics from a raster map based on vector polygon map and uploads statistics to new attribute columns, see *v.rast.stats*.

## Example

In this example, the raster polygon map basins in the North Carolina sample dataset is used to calculate raster statistics for zones for elevation raster map:

`g.region raster=basins -p`

This will set and print computational region in the format:

```
projection: 99 (Lambert Conformal Conic)
zone: 0
datum: nad83
ellipsoid: a=6378137 es=0.006694380022900787
north: 228500
south: 215000
west: 630000
east: 645000
nsres: 10
ewres: 10
rows: 1350
cols: 1500
cells: 2025000
```

Check basin’s IDs using:

`r.category basins`

This will print them in the format:

```
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
```

Visualization of them underlying elevation map can be created as:

```
d.mon wx0
d.rast map=elevation
r.colors map=elevation color=grey
d.rast map=basins
r.colors map=basins color=bgyr
d.legend raster=basins use=2,4,6,8,10,12,14,16,18,20,22,24,26,28,30
d.barscale
```

Figure: Zones (basins, opacity: 60%) with underlying elevation map for North Carolina sample dataset.

Then statistics for elevation can be calculated separately for every zone, i.e. basin found in the **zones** parameter:

```
r.univar -t map=elevation zones=basins separator=comma \
output=basin_elev_zonal.csv
```

This will print information in the format:

```
zone,label,non_null_cells,null_cells,min,max,range,mean,mean_of_abs,
stddev,variance,coeff_var,sum,sum_abs2,,116975,0,55.5787925720215,
133.147018432617,77.5682258605957,92.1196971445722,92.1196971445722,
15.1475301152556,229.447668592576,16.4433129773355,10775701.5734863,
10775701.57348634,,75480,0,61.7890930175781,110.348838806152,
48.5597457885742,83.7808205765268,83.7808205765268,11.6451777476995,
135.610164775515,13.8995747088232,6323776.33711624,6323776.33711624
6,,1137,0,66.9641571044922,83.2070922851562,16.2429351806641,
73.1900814395257,73.1900814395257,4.15733292896409,17.2834170822492,
5.68018623179036,83217.1225967407,83217.12259674078,,80506,
0,67.4670791625977,147.161514282227, ...
```

Comma Separated Values (CSV) file is best viewed through a spreadsheet program such as Microsoft Excel, Libre/Open Office Calc or Google Docs:

Figure: Raster statistics for zones (basins, North Carolina sample dataset) viewed through Libre/Open Office Calc

## Todo

To be implemented *mode, skewness, kurtosis*.

## See Also

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

## Authors

Hamish Bowman, Otago University, New Zealand

Extended statistics by Martin Landa

Multiple input map support by Ivan Shmakov

Zonal loop by Markus Metz

*Last changed: $Date: 2015-09-02 13:27:57 +0200 (Wed, 02 Sep 2015) $*

Main index | Raster index | Topics index | Keywords index | Full index

© 2003-2016 GRASS Development Team, GRASS GIS 7.0.4 Reference Manual