1v.db.univar(1) GRASS GIS User's Manual v.db.univar(1)
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6 v.db.univar - Calculates univariate statistics on selected table col‐
7 umn for a GRASS vector map.
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10 vector, statistics, attribute table
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13 v.db.univar
14 v.db.univar --help
15 v.db.univar [-eg] map=name [layer=string] column=name
16 [where=sql_query] [percentile=float[,float,...]] [format=string]
17 [--help] [--verbose] [--quiet] [--ui]
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19 Flags:
20 -e
21 Extended statistics (quartiles and 90th percentile)
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23 -g
24 Print stats in shell script style
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26 --help
27 Print usage summary
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29 --verbose
30 Verbose module output
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32 --quiet
33 Quiet module output
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35 --ui
36 Force launching GUI dialog
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38 Parameters:
39 map=name [required]
40 Name of vector map
41 Or data source for direct OGR access
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43 layer=string
44 Layer number or name
45 Vector features can have category values in different layers. This
46 number determines which layer to use. When used with direct OGR ac‐
47 cess this is the layer name.
48 Default: 1
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50 column=name [required]
51 Name of attribute column on which to calculate statistics (must be
52 numeric)
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54 where=sql_query
55 WHERE conditions of SQL statement without ’where’ keyword
56 Example: income < 1000 and population >= 10000
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58 percentile=float[,float,...]
59 Percentile to calculate (requires extended statistics flag)
60 Options: 0-100
61 Default: 90
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63 format=string
64 Output format
65 Options: plain, json, shell
66 plain: Plain text output
67 json: JSON (JavaScript Object Notation)
68 shell: Shell script style for Bash eval
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71 v.db.univar calculates basic univariate statistics for numeric at‐
72 tributes in a vector attribute table. It will calculate minimum, maxi‐
73 mum, range, mean, standard deviation, variance, coefficient of varia‐
74 tion, quartiles, median, and 90th percentile.
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76 v.db.univar uses db.univar which in turn uses db.select to get the at‐
77 tribute values on which it calculates the statistics. This means that
78 statistics are calculated based on the entries in the attribute table,
79 not based on the features in the map. One attribute value is read from
80 each line in the attribute table, whether there are no, one or several
81 features with the category value referenced by that line, or whether
82 any features have more than one category value. For feature-based, in‐
83 stead of attribute table-based, univariate statistics on attributes see
84 v.univar. NOTES A database connection must be defined for the selected
85 vector layer.
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88 Univariate statistics on attribute table column
89 In this example, the 30 years precipitation data table is statistically
90 analysed (North Carolina sample dataset) and univariate statistics per‐
91 formed:
92 # show columns of attribute table connected to precipitation map
93 v.info -c precip_30ynormals
94 # univariate statistics on 30 years annual precipitation in NC
95 v.db.univar precip_30ynormals column=annual
96 Number of values: 136
97 Minimum: 947.42
98 Maximum: 2329.18
99 Range: 1381.76
100 Mean: 1289.31147058823
101 [...]
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103 Univariate statistics on randomly sampled data points
104 In this example, random points are sampled from the elevation map
105 (North Carolina sample dataset) and univariate statistics performed:
106 g.region raster=elevation -p
107 v.random output=samples n=100
108 v.db.addtable samples column="heights double precision"
109 v.what.rast samples raster=elevation column=heights
110 v.db.select samples
111 v.db.univar samples column=heights
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113 JSON output
114 This uses the JSON output of the module which is passed using a pipe
115 (in Bash or other unix-like shell) to the jq tool which selects just
116 the relevant statistic.
117 v.db.univar precip_30ynormals column=annual format=json | jq .statistics.mean
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120 db.univar, r.univar, v.univar, db.select, d.vect.thematic, v.random
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122 GRASS SQL interface
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125 Michael Barton, Arizona State University
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127 and authors of r.univar.sh (Markus Neteler et al.)
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130 Available at: v.db.univar source code (history)
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132 Accessed: Saturday Oct 28 18:19:21 2023
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134 Main index | Vector index | Topics index | Keywords index | Graphical
135 index | Full index
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137 © 2003-2023 GRASS Development Team, GRASS GIS 8.3.1 Reference Manual
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141GRASS 8.3.1 v.db.univar(1)