|v.db.univar(1grass)||GRASS GIS User's Manual||v.db.univar(1grass)|
v.db.univar - Calculates univariate statistics on selected table column for a GRASS vector map.
vector, statistics, attribute table
v.db.univar [-eg] map=name [layer=string] column=name [where=sql_query] [percentile=float[,float,...]] [--help] [--verbose] [--quiet] [--ui]
- map=name [required]
Name of vector map
Or data source for direct OGR access
Layer number or name
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
- column=name [required]
Name of attribute column on which to calculate statistics (must be numeric)
WHERE conditions of SQL statement without ’where’ keyword
Example: income < 1000 and population >= 10000
Percentile to calculate (requires extended statistics flag)
v.db.univar calculates basic univariate statistics for numeric attributes in a vector attribute table. It will calculate minimum, maximum, range, mean, standard deviation, variance, coefficient of variation, quartiles, median, and 90th percentile.
v.db.univar uses db.univar which in turn uses db.select to get the attribute values on which it calculates the statistics. This means that statistics are calculated based on the entries in the attribute table, not based on the features in the map. One attribute value is read from each line in the attribute table, whether there are no, one or several features with the category value referenced by that line, or whether any features have more than one category value. For feature-based, instead of attribute table-based, univariate statistics on attributes see v.univar. NOTES A database connection must be defined for the selected vector layer.
Univariate statistics on attribute table column¶
In this example, the 30 years precipitation data table is
statistically analysed (North Carolina sample dataset) and univariate
# show columns of attribute table connected to precipitation map v.info -c precip_30ynormals # univariate statistics on 30 years annual precipitation in NC v.db.univar precip_30ynormals column=annual
Number of values: 136
Univariate statistics on randomly sampled data points¶
In this example, random points are sampled from the elevation map
(North Carolina sample dataset) and univariate statistics performed:
g.region raster=elevation -p v.random output=samples n=100 v.db.addtable samples column="heights double precision" v.what.rast samples raster=elevation column=heights v.db.select samples v.db.univar samples column=heights
db.univar, r.univar, v.univar, db.select, d.vect.thematic, v.random
Michael Barton, Arizona State University
and authors of r.univar.sh (Markus Neteler et al.)
Available at: v.db.univar source code (history)
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© 2003-2021 GRASS Development Team, GRASS GIS 7.8.6 Reference Manual