You can just coerce the data back into a
SpatialPolygonsDataFrame and add the attributes back to the data. You just have to index the original data.frame rows so you know what to relate back to the data.
One issue with your example data is that it is a multipart geometry (multiple polygons collapsed into a single feature and attribute). I am going to explode the geometry so that each polygon is represented individually. The example will still work if this step is not done but it provides a better example in showing how attribute tracking is happening.
First, add packages and data.
st <- tigris::states(cb=T)
hawaii <- subset(st,STATEFP=="15")
You will see that the dimensions currently indicate that there is only one feature with nine attribute columns. Here, we are going to explode the geometry so that we have the actual number of polygons (n=28). We use sf to do this but coerce back to an sp object at the end.
( x <- as(hawaii, "sf") )
( x <- sf::st_cast(x, substring("MULTIPOLYGON", 6, last = 1000000L)) )
hawaii <- as(x, "Spatial")
Now we can go back to the example at hand by creating a bounding polygon and then clipping to it. Note that I am using the
id = rownames(hawaii@data) argument in
gIntersection to ensure that the polygon ids match the rownames in the
sp.df data.frame object that we set aside. Looking at the names of the resulting hawaii
SpatialPolygons object will show that they match the original rownames in the @data slot of the original data and those of
e <- as(extent(-178.3347+18, -154.8068, 18.91036, 28.40212),
proj4string(e) <- proj4string(hawaii)
sp.df <- hawaii@data
hawaii <- gIntersection(e, hawaii, byid = TRUE,
id = rownames(hawaii@data),
drop_lower_td = TRUE)
We can now coerce the data back to a
SpatialPolygonsDataFrame and use the
sp.df data.frame in the data argument. We can use
%in% to match
names(hawaii). Looking at the object dimensions again we see that there are now 11 features (polygons) with 9 attribute columns.
hawaii <- SpatialPolygonsDataFrame(hawaii,
data = sp.df[which(rownames(sp.df) %in% names(hawaii)),])