Provided by: grass-doc_7.8.2-1build3_all 
NAME
v.univar - Calculates univariate statistics of vector map features.
Variance and standard deviation is calculated only for points if specified.
KEYWORDS
vector, statistics, univariate statistics, attribute table, geometry
SYNOPSIS
v.univar
v.univar --help
v.univar [-gewd] map=name [layer=string] [type=string[,string,...]] [column=name]
[where=sql_query] [percentile=integer] [--help] [--verbose] [--quiet] [--ui]
Flags:
-g
Print the stats in shell script style
-e
Calculate extended statistics
-w
Weigh by line length or area size
-d
Calculate geometric distances instead of attribute statistics
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
map=name [required]
Name of vector map
Or data source for direct OGR access
layer=string
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.
Default: 1
type=string[,string,...]
Input feature type
Options: point, line, boundary, centroid, area
Default: point,line,area
column=name
Name of attribute column
where=sql_query
WHERE conditions of SQL statement without ’where’ keyword
Example: income < 1000 and population >= 10000
percentile=integer
Percentile to calculate (requires extended statistics flag)
Options: 0-100
Default: 90
DESCRIPTION
v.univar calculates univariate statistics on (by default) an attribute of, or, through the
-d flag on distance between, vector map features. Attributes are read per feature and per
category value. This means that if the map contains several features with the same
category value, the attribute is read as many times as there are features. On the other
hand, if a feature has more than one category value, each attribute value linked to each
of the category values of the feature is read. For statistics on one attribute per
category value, instead of one attribute per feature and per category, see v.db.univar.
Extended statistics (-e) adds median, 1st and 3rd quartiles, and 90th percentile to the
output.
NOTES
When using the -d flag, univariate statistics of distances between vector features are
calculated. The distances from all features to all other features are used. Since the
distance from feature A to feature B is the same like the distance from feature B to
feature A, that distance is considered only once, i.e. all pairwise distances between
features are used. Depending on the selected vector type, distances are calculated as
follows:
• type=point: point distances are considered;
• type=line: line to line distances are considered;
• type=area: not supported, use type=centroid instead (and see v.distance for
calculating distances between areas)
EXAMPLES
The examples are based on the North Carolina sample dataset.
Example dataset preparation
g.region raster=elevation -p
v.random output=samples npoints=100
v.db.addtable map=samples columns="heights double precision"
v.what.rast map=samples rast=elevation column=heights
v.db.select map=samples
Calculate height attribute statistics
v.univar -e samples column=heights type=point
number of features with non NULL attribute: 100
number of missing attributes: 0
number of NULL attributes: 0
minimum: 57.2799
maximum: 148.903
range: 91.6235
sum: 10825.6
mean: 108.256
mean of absolute values: 108.256
population standard deviation: 20.2572
population variance: 410.356
population coefficient of variation: 0.187123
sample standard deviation: 20.3593
sample variance: 414.501
kurtosis: -0.856767
skewness: 0.162093
1st quartile: 90.531
median (even number of cells): 106.518
3rd quartile: 126.274
90th percentile: 135.023
Compare to statistics of original raster map
r.univar -e elevation
total null and non-null cells: 2025000
total null cells: 0
Of the non-null cells:
----------------------
n: 2025000
minimum: 55.5788
maximum: 156.33
range: 100.751
mean: 110.375
mean of absolute values: 110.375
standard deviation: 20.3153
variance: 412.712
variation coefficient: 18.4057 %
sum: 223510266.558102
1st quartile: 94.79
median (even number of cells): 108.88
3rd quartile: 126.792
90th percentile: 138.66
Calculate statistic of distance between sampling points
v.univar -d samples type=point
number of primitives: 100
number of non zero distances: 4851
number of zero distances: 0
minimum: 69.9038
maximum: 18727.7
range: 18657.8
sum: 3.51907e+07
mean: 7254.33
mean of absolute values: 7254.33
population standard deviation: 3468.53
population variance: 1.20307e+07
population coefficient of variation: 0.478132
sample standard deviation: 3468.89
sample variance: 1.20332e+07
kurtosis: -0.605406
skewness: 0.238688
SEE ALSO
db.univar, r.univar, v.db.univar, v.distance, v.neighbors, v.qcount
AUTHORS
Radim Blazek, ITC-irst
extended by:
Hamish Bowman, University of Otago, New Zealand
Martin Landa
SOURCE CODE
Available at: v.univar source code (history)
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