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<table width="100%" summary="page for st_collection_extract {sf}"><tr><td>st_collection_extract {sf}</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Given an object with geometries of type <code>GEOMETRY</code> or <code>GEOMETRYCOLLECTION</code>,
return an object consisting only of elements of the specified type.</h2>

<h3>Description</h3>

<p>Similar to ST_CollectionExtract in PostGIS. If there are no sub-geometries
of the specified type, an empty geometry is returned.
</p>

<h3>Usage</h3>

<pre>
st_collection_extract(
  x,
  type = c("POLYGON", "POINT", "LINESTRING"),
  warn = FALSE
)

## S3 method for class 'sfg'
st_collection_extract(
  x,
  type = c("POLYGON", "POINT", "LINESTRING"),
  warn = FALSE
)

## S3 method for class 'sfc'
st_collection_extract(
  x,
  type = c("POLYGON", "POINT", "LINESTRING"),
  warn = FALSE
)

## S3 method for class 'sf'
st_collection_extract(
  x,
  type = c("POLYGON", "POINT", "LINESTRING"),
  warn = FALSE
)
</pre>

<h3>Arguments</h3>

<table summary="R argblock">
<tr valign="top"><td><code>x</code></td>
<td>
<p>an object of class <code>sf</code>, <code>sfc</code> or <code>sfg</code> that has
mixed geometry (<code>GEOMETRY</code> or <code>GEOMETRYCOLLECTION</code>).</p>
</td></tr>
<tr valign="top"><td><code>type</code></td>
<td>
<p>character; one of &quot;POLYGON&quot;, &quot;POINT&quot;, &quot;LINESTRING&quot;</p>
</td></tr>
<tr valign="top"><td><code>warn</code></td>
<td>
<p>logical; if <code>TRUE</code>, warn if attributes are assigned to
sub-geometries when casting (see <code><a href="st_cast.html">st_cast</a></code>)</p>
</td></tr>
</table>

<h3>Value</h3>

<p>An object having the same class as <code>x</code>, with geometries
consisting only of elements of the specified type.
For <code>sfg</code> objects, an <code>sfg</code> object is returned if there is only
one geometry of the specified type, otherwise the geometries are combined
into an <code>sfc</code> object of the relevant type. If any subgeometries in the
input are MULTI, then all of the subgeometries in the output will be MULTI.
</p>

<h3>Examples</h3>

<pre>
pt &lt;- st_point(c(1, 0))
ls &lt;- st_linestring(matrix(c(4, 3, 0, 0), ncol = 2))
poly1 &lt;- st_polygon(list(matrix(c(5.5, 7, 7, 6, 5.5, 0, 0, -0.5, -0.5, 0), ncol = 2)))
poly2 &lt;- st_polygon(list(matrix(c(6.6, 8, 8, 7, 6.6, 1, 1, 1.5, 1.5, 1), ncol = 2)))
multipoly &lt;- st_multipolygon(list(poly1, poly2))

i &lt;- st_geometrycollection(list(pt, ls, poly1, poly2))
j &lt;- st_geometrycollection(list(pt, ls, poly1, poly2, multipoly))

st_collection_extract(i, "POLYGON")
st_collection_extract(i, "POINT")
st_collection_extract(i, "LINESTRING")

## A GEOMETRYCOLLECTION
aa &lt;- rbind(st_sf(a=1, geom = st_sfc(i)),
			st_sf(a=2, geom = st_sfc(j)))

## With sf objects
st_collection_extract(aa, "POLYGON")
st_collection_extract(aa, "LINESTRING")
st_collection_extract(aa, "POINT")

## With sfc objects
st_collection_extract(st_geometry(aa), "POLYGON")
st_collection_extract(st_geometry(aa), "LINESTRING")
st_collection_extract(st_geometry(aa), "POINT")

## A GEOMETRY of single types
bb &lt;- rbind(
	st_sf(a = 1, geom = st_sfc(pt)),
	st_sf(a = 2, geom = st_sfc(ls)),
	st_sf(a = 3, geom = st_sfc(poly1)),
	st_sf(a = 4, geom = st_sfc(multipoly))
)

st_collection_extract(bb, "POLYGON")

## A GEOMETRY of mixed single types and GEOMETRYCOLLECTIONS
cc &lt;- rbind(aa, bb)

st_collection_extract(cc, "POLYGON")

</pre>

<hr /><div style="text-align: center;">[Package <em>sf</em> version 0.9-5 <a href="00Index.html">Index</a>]</div>
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