I am trying to draw a plot in R that its x axis and y axis have an arrow in their tips. I googled it and did not found anything helpful. I found it how to do it in Python in this page.
I want something like this picture:
My attempt:
I remove the plot frame and add axis separately.
x=seq(0,5,by=.1)
y=x*x
plot(x, y, axes = FALSE, frame.plot = FALSE, type="l")
box(bty="l")
axis(1)
axis(2)
Function Arrowhead from package shape draws arrowhead-shaped polygons centered at user-supplied points. To draw arrowheads at the top left and bottom right corners of the plot region pointing in the direction of your axes, you can do:
usr <- par("usr")
shape::Arrowhead(
x0 = usr[1:2],
y0 = usr[4:3],
angle = c(90, 0),
xpd = TRUE
)
where par("usr") is a vector c(left, right, bottom, top) specifying the boundary of the plot region in user coordinates. xpd = TRUE ensures that arrowheads are not clipped to the plot region.
If you want to avoid installing a package, then note that base R has arrows, but it does not draw filled arrowheads and it complains if you ask for a zero-length arrow (i.e., an arrow with a head but no shaft). One way around the latter issue is to draw arrows that are collinear with the axes:
usr <- par("usr")
arrows(
x0 = usr[1L],
x1 = usr[1:2],
y0 = usr[3L],
y1 = usr[4:3],
length = 0.1,
angle = 20,
xpd = TRUE
)
As you might expect, both functions have optional arguments that you can use to adjust the appearance of the arrow(head)s.
Related
I've added an verticle line at some point on x-axis (as shown in line plot of below Fig.) using abline() function in R, and I want to either put a legend for it or add some text over it (vertically on the abline).
So, is it possible to do this? If yes, then how I can do this?
Use text with the indicated arguments. Alternately use the legend function as shown.
abline is classic graphics so it is assumed you want to use that plotting system but if you want ggplot2 see Add a horizontal line to plot and legend in ggplot2 and make the obvious modifications to change the horizontal line to vertical.
x <- y <- 1:10; v <- 5 # input
plot(x, y)
abline(v = v, col = "red")
text("Vertical Line", x = v, y = max(y), srt = -90, pos = 4) # near top
text("Vertical Line", x = v, y = min(y), srt = 90, adj = c(0, -0.5)) # near bottom
legend("topleft", legend = "Vertical Line", pch = "|", col = "red")
Here is the problem:
x<-seq(0,10,length.out = 1000)
y1<-dnorm(x,mean = 2,sd=1)
y2<-dnorm(x,mean = 6,sd=1)
plot(x,y1,type="l")
lines(x,y2)
abline(v=x[380])
The graph is shown below. How can I fill 2 different colors, say red and blue, on the each side of vertical line but still below two normal density functions. I thought I can use polygon, but failed.
This is the graph without filling colors:
Here's one way:
First, we'll get the parallel minimum of your densities - this is a vector of the top y coordinates for our polygons.
y = pmin(y1, y2)
# set up your plot as in the question
plot(x, y1, type="l")
lines(x, y2)
# define a re-usable variable for the vertical line placement
x_vert = 380
abline(v = x[x_vert])
# Now we'll draw 2 polygons, one for the left side, one for the right.
# The first (x,y) pairs of the polygon are just the (x,y) coords of the
# density we're filling to, until the vertical line
# Then we need to connect the "bottom" points, which have coordinates
# (x[x_vert], 0) and (x[1], 0)
polygon(x = c(x[1:x_vert], x[x_vert], x[1]),
y = c(y[1:x_vert], 0, 0),
col = "blue")
# similar for the right hand polygon, but now going from x_vert to length(x)
polygon(x = c(x[x_vert:length(x)], x[length(x)], x[x_vert]),
y = c(y[x_vert:length(x)], 0, 0),
col = "red")
Voila!
I used this code to make this plot:
plot(p, cv2,col=rgb(0,100,0,50,maxColorValue=255),pch=16,
panel.last=abline(h=67,v=1.89, lty=1,lwd=3))
My plot looks like this:
1.) How can I plot the value of the ablines in a simple plot?
2.) How can I scale my plot so that both lines appear in the middle?
to change scale of plot so lines are in the middle change the axes i.e.
x<-1:10
y<-1:10
plot(x,y)
abline(a=1,b=0,v=1)
changed to:
x<-1:10
y<-1:10
plot(x,y,xlim=c(-30,30))
abline(a=1,b=0,v=1)
by "value" I am assuming you mean where the line cuts the x-axis? Something like text? i.e.:
text((0), min(y), "number", pos=2)
if you want the label on the x axis then try:
abline(a=1,b=0,v=1)
axis(1, at=1,labels=1)
to prevent overlap between labels you could remove the zero i.e.:
plot(x,y,xlim=c(-30,30),yaxt="n")
axis(2, at=c(1.77,5,10,15,20,25))
or before you plot extend the margins and add the labels further from the axis
par(mar = c(6.5, 6.5, 6.5, 6.5))
plot(x,y,xlim=c(-30,30))
abline(a=1,b=0,v=1)
axis(2, at=1.77,labels=1.77,mgp = c(10, 2, 0))
Similar in spirit to the answer proposed by #user1317221, here is my suggestion
# generate some fake points
x <- rnorm(100)
y <- rnorm(100)
# positions of the lines
vert = 0.5
horiz = 1.3
To display the lines at the center of the plot, first compute the horizontal and vertical distances between the data points and the lines, then adjust the limits adequately.
# compute the limits, in order for the lines to be centered
# REM we add a small fraction (here 10%) to leave some empty space,
# available to plot the values inside the frame (useful for one the solutions, see below)
xlim = vert + c(-1.1, 1.1) * max(abs(x-vert))
ylim = horiz + c(-1.1, 1.1) * max(abs(y-horiz))
# do the main plotting
plot(x, y, xlim=xlim, ylim=ylim)
abline(h=horiz, v=vert)
Now, you could plot the 'values of the lines', either on the axes (the lineparameter allows you to control for possible overlapping):
mtext(c(vert, horiz), side=c(1,2))
or alternatively within the plotting frame:
text(x=vert, y=ylim[1], labels=vert, adj=c(1.1,1), col='blue')
text(x=xlim[1], y=horiz, labels=horiz, adj=c(0.9,-0.1), col='blue')
HTH
How do I change the background color for a plot, only for a specific area?
For example, from x=2 to x=4?
Bonus question: is it also possible for a combination of x and y coordinates? (for example from (1,2) to (3,4))?
Many thanks!
This can be achieved by thinking about the plot somewhat differently to your description. Basically, you want to draw a coloured rectangle between the desired positions on the x-axis, filling the entire y-axis limit range. This can be achieved using rect(), and note how, in the example below, I grab the user (usr) coordinates of the current plot to give me the limits on the y-axis and that we draw beyond these limits to ensure the full range is covered in the plot.
plot(1:10, 1:10, type = "n", axes = FALSE) ## no axes
lim <- par("usr")
rect(2, lim[3]-1, 4, lim[4]+1, border = "red", col = "red")
axis(1) ## add axes back
axis(2)
box() ## and the plot frame
rect() can draw a sequence of rectangles if we provide a vector of coordinates, and it can easily handle the case for the arbitrary x,y coordinates of your bonus, but for the latter it is easier to avoid mistakes if you start with a vector of X coordinates and another for the Y coordinates as below:
X <- c(1,3)
Y <- c(2,4)
plot(1:10, 1:10, type = "n", axes = FALSE) ## no axes
lim <- par("usr")
rect(X[1], Y[1], X[2], Y[2], border = "red", col = "red")
axis(1) ## add axes back
axis(2)
box() ## and the plot frame
You could just as easily have the data as you have it in the bonus:
botleft <- c(1,2)
topright <- c(3,4)
plot(1:10, 1:10, type = "n", axes = FALSE) ## no axes
lim <- par("usr")
rect(botleft[1], botleft[2], topright[1], topright[2], border = "red",
col = "red")
axis(1) ## add axes back
axis(2)
box() ## and the plot frame
I am trying to add arrows marking specific x coordinates below the x axis in an R plot. My x axis is at y=0 and when I try to use negative y-coordinates in arrows, so the arrows will be perpendicular to x axis, I get only the very edges of the arrow plotted (although is some space, e,g where the x-axis label and tickmarks are plotted).
The xpd option can be used in arrows so you can just set your coordinates to be outside your plot region and set xpd to TRUE. For example, assuming xlim = c(0,10) and ylim = (0,10), and you set the x-axis to 0 then
arrows(1.4, -1, 1.4, 0, xpd = TRUE)
draws a vertical arrow pointing up at the x-axis at position 1.4 on that axis.
You can do this by adding an extra overlay, by calling par(new=TRUE), with reduced margins. For example:
plot(1,1) ## start a plot
opar <- par(new = TRUE, ## add a new layer
mar = c(0,0,0,0)) ## with no margins margins
## set up the plotting area for this layer
plot(1,1,xlim=c(0,1),ylim=c(0,1),type='n',xlab='',ylab='')
arrows(0.1,0.05,0.5,0.05) ## add arrow
par(opar) ## return the plot parameters to their prior values
Edit: If you want to keep the same coordinates as in the original plot, you have to choose the x- and y-axis limits carefully. This is illustrated belo:
plot(1,1,xlim=0:1,ylim=0:1)
arrows(0.1,0.05,0.5,0.05)
gpar <- par()
opar <- par(new = TRUE, mar = c(0,0,0,0),xaxs='i',yaxs='i')
m1 <- (gpar$usr[2] - gpar$usr[1])/(gpar$plt[2] - gpar$plt[1])
c1 <- gpar$usr[1] - m1*gpar$plt[1]
m2 <- (gpar$usr[4] - gpar$usr[3])/(gpar$plt[4] - gpar$plt[3])
c2 <- gpar$usr[3] - m2*gpar$plt[3]
xlim <- c(c1, m1 + c1)
ylim <- c(c2, m2 + c2)
plot(1,1,xlim=xlim,ylim=ylim,type='n',xlab='',ylab='')
arrows(0.1,0.05,0.5,0.05,col='red')
points(1,1,col='red')
par(opar)