Graphics Reference
In-Depth Information
# Keep 1 out of every 'by' values in vector x
every_n
<-
function
function
(x, by
=
2
) {
x
<-
sort(x)
x[seq(
1
, length(x), by
=
by)]
}
# Keep 1 of every 4 values in x and y
keepx
<-
every_n(unique(isabel$x), by
=
4
)
keepy
<-
every_n(unique(isabel$y), by
=
4
)
# Keep only those rows where x value is in keepx and y value is in keepy
islicesub
<-
subset(islice, x
%in%
keepx
&
y
%in%
keepy)
Now that we've taken a subset of the data, we can plot it, with arrowheads, as shown in
Fig-
# Need to load grid for arrow() function
library(grid)
# Make the plot with the subset, and use an arrowhead 0.1 cm long
ggplot(islicesub, aes(x
=
x, y
=
y))
+
geom_segment(aes(xend
=
x
+
vx
/
50
, yend
=
y
+
vy
/
50
),
arrow
=
arrow(length
=
unit(
0.1
,
"cm"
)), size
=
0.25
)
