Scatter plots are useless when number of plots is large.
So, e.g., using normal approximation, we can get the contour plot.
My question: Is there any package to implement the contour plot from scatter plot.
Thank you #G5W !! I can do it !!
You don't offer any data, so I will respond with some artificial data,
constructed at the bottom of the post. You also don't say how much data
you have although you say it is a large number of points. I am illustrating
with 20000 points.
You used the group number as the plotting character to indicate the group.
I find that hard to read. But just plotting the points doesn't show the
groups well. Coloring each group a different color is a start, but does
not look very good.
plot(x,y, pch=20, col=rainbow(3)[group])
Two tricks that can make a lot of points more understandable are:
1. Make the points transparent. The dense places will appear darker. AND
2. Reduce the point size.
plot(x,y, pch=20, col=rainbow(3, alpha=0.1)[group], cex=0.8)
That looks somewhat better, but did not address your actual request.
Your sample picture seems to show confidence ellipses. You can get
those using the function dataEllipse from the car package.
library(car)
plot(x,y, pch=20, col=rainbow(3, alpha=0.1)[group], cex=0.8)
dataEllipse(x,y,factor(group), levels=c(0.70,0.85,0.95),
plot.points=FALSE, col=rainbow(3), group.labels=NA, center.pch=FALSE)
But if there are really a lot of points, the points can still overlap
so much that they are just confusing. You can also use dataEllipse
to create what is basically a 2D density plot without showing the points
at all. Just plot several ellipses of different sizes over each other filling
them with transparent colors. The center of the distribution will appear darker.
This can give an idea of the distribution for a very large number of points.
plot(x,y,pch=NA)
dataEllipse(x,y,factor(group), levels=c(seq(0.15,0.95,0.2), 0.995),
plot.points=FALSE, col=rainbow(3), group.labels=NA,
center.pch=FALSE, fill=TRUE, fill.alpha=0.15, lty=1, lwd=1)
You can get a more continuous look by plotting more ellipses and leaving out the border lines.
plot(x,y,pch=NA)
dataEllipse(x,y,factor(group), levels=seq(0.11,0.99,0.02),
plot.points=FALSE, col=rainbow(3), group.labels=NA,
center.pch=FALSE, fill=TRUE, fill.alpha=0.05, lty=0)
Please try different combinations of these to get a nice picture of your data.
Additional response to comment: Adding labels
Perhaps the most natural place to add group labels is the centers of the
ellipses. You can get that by simply computing the centroids of the points in each group. So for example,
plot(x,y,pch=NA)
dataEllipse(x,y,factor(group), levels=c(seq(0.15,0.95,0.2), 0.995),
plot.points=FALSE, col=rainbow(3), group.labels=NA,
center.pch=FALSE, fill=TRUE, fill.alpha=0.15, lty=1, lwd=1)
## Now add labels
for(i in unique(group)) {
text(mean(x[group==i]), mean(y[group==i]), labels=i)
}
Note that I just used the number as the group label, but if you have a more elaborate name, you can change labels=i to something like
labels=GroupNames[i].
Data
x = c(rnorm(2000,0,1), rnorm(7000,1,1), rnorm(11000,5,1))
twist = c(rep(0,2000),rep(-0.5,7000), rep(0.4,11000))
y = c(rnorm(2000,0,1), rnorm(7000,5,1), rnorm(11000,6,1)) + twist*x
group = c(rep(1,2000), rep(2,7000), rep(3,11000))
You can use hexbin::hexbin() to show very large datasets.
#G5W gave a nice dataset:
x = c(rnorm(2000,0,1), rnorm(7000,1,1), rnorm(11000,5,1))
twist = c(rep(0,2000),rep(-0.5,7000), rep(0.4,11000))
y = c(rnorm(2000,0,1), rnorm(7000,5,1), rnorm(11000,6,1)) + twist*x
group = c(rep(1,2000), rep(2,7000), rep(3,11000))
If you don't know the group information, then the ellipses are inappropriate; this is what I'd suggest:
library(hexbin)
plot(hexbin(x,y))
which produces
If you really want contours, you'll need a density estimate to plot. The MASS::kde2d() function can produce one; see the examples in its help page for plotting a contour based on the result. This is what it gives for this dataset:
library(MASS)
contour(kde2d(x,y))
I am trying to simulate a minefield by plotting two Poisson distributed samples in the same plot, one with a higher intensity and smaller area than the other. This is the minefield and the other is just noise (stones, holes, metal) seen as points. I cannot get R to plot the points with the same units in the axis. Whatever I do, the points span the entire plot, even though I only want the X points to cover a quarter of the plot. My R-code is just the following:
library(spatstat)
Y = rpoispp(c(5),win=owin(c(0,10),c(0,10)))
X = rpoispp(c(10),win=owin(c(0,5),c(0,5)))
Please let me know if you can help me.
My guess is that you are doing something like:
> plot(Y)
> plot(X)
to plot the points.
The problem with this is that the default behavior of the plot function for the class ppp (which is what the rpoispp function returns) is to create a new plot with just its points. So the second plot call essentially erases the first plot, and plots its own points in a differently scaled window. You can override this behavior by setting the option add=TRUE for the second plot. So the code
> plot(Y)
> plot(X, add=TRUE, cols="red")
should get you something like:
Check out the docs (help(plot.ppp)) for more explanation and other options to prettify the plot.
Hi I got a data frame weekly.mean.values with the following structure:
week:mean:ci.lower:ci.upper
Where week is a factor; mean, ci.lower and ci.upper are numeric. For each week, there is only one mean, and one ci.lower or ci.upper.
I was trying to plot a shaded area inside of the 95% confidence interval around the mean, with the following code:
ggplot(weekly.mean.values,aes(x=week,y=mean)) +
geom_line() +
geom_ribbon(aes(ymin=ci.lower,ymax=ci.upper))
The plot, however, came out blank (that is only with x-axis and y-axis present, but no lines, or points, let alone shaded areas).
If I removed the geom_ribbon part, I did get a line. I know that this should be a very simple task but I don't know why I couldn't get geom_ribbon to plot what I wanted. Any hint would be truly appreciated.
I realize this thread is super old, but google still find it.
The answer is that you need to set the ymin and ymax to use a part of the data you are using on the y-axis. It you set them to scalar values then the ribbon covers the entire plot from top to bottom.
You can use
ymin=0
ymax=mean
to go from 0 to your y-point or even
ymin=mean-1
ymax=mean+1
to have the ribbon cover a strip encompassing your actual data.
I may be missing something, but the ribbon will be plotted filled with grey20 by default. You are plotting this layer on top of the data so no wonder it obscures it. Also, it is also possible that the limits for the plot axes derived from the data provided to the initial ggplot() call will not be sufficient to contain the confidence interval ribbon. In that case, I would not be surprised to see a grey/blank plot.
To see if this is the problem, try altering your geom_ribbon() line to:
geom_ribbon(aes(ymin=ci.lower,ymax=ci.upper), alpha = 0.5)
which will plot the ribbon with transparency whic should show the data underneath if the problem is what I think it is.
If so, set the x and y limits to the range of the data +/- the confidence interval you wish to plot and swap the order of the layers (i.e. draw the line on top of the ribbon), and use transparency in the ribbon to show the grid through it.
From ggplot's docs for geom_ribbon (2.1.0):
For each continuous x value, geom_interval displays a y interval. geom_area is a special case of geom_ribbon, where the minimum of the range is fixed to 0.
In this case, x values cannot be factors for geom_ribbon. One solution would be to convert week from a factor to a numeric. e.g.
ggplot(weekly.mean.values,aes(x=as.numeric(week),y=mean)) +
geom_line() +
geom_ribbon(aes(ymin=ci.lower,ymax=ci.upper))
geom_line should handle the switch from factor to numeric without incident, although the X axis scale may display differently.
I have two related problems.
Problem 1: I'm currently using the code below to generate a histogram overlayed with a density plot:
hist(x,prob=T,col="gray")
axis(side=1, at=seq(0,100, 20), labels=seq(0,100,20))
lines(density(x))
I've pasted the data (i.e. x above) here.
I have two issues with the code as it stands:
the last tick and label (100) of the x-axis does not appear on the histogram/plot. How can I put these on?
I'd like the y-axis to be of count or frequency rather than density, but I'd like to retain the density plot as an overlay on the histogram. How can I do this?
Problem 2: using a similar solution to problem 1, I now want to overlay three density plots (not histograms), again with frequency on the y-axis instead of density. The three data sets are at:
http://pastebin.com/z5X7yTLS
http://pastebin.com/Qg8mHg6D
http://pastebin.com/aqfC42fL
Here's your first 2 questions:
myhist <- hist(x,prob=FALSE,col="gray",xlim=c(0,100))
dens <- density(x)
axis(side=1, at=seq(0,100, 20), labels=seq(0,100,20))
lines(dens$x,dens$y*(1/sum(myhist$density))*length(x))
The histogram has a bin width of 5, which is also equal to 1/sum(myhist$density), whereas the density(x)$x are in small jumps, around .2 in your case (512 even steps). sum(density(x)$y) is some strange number definitely not 1, but that is because it goes in small steps, when divided by the x interval it is approximately 1: sum(density(x)$y)/(1/diff(density(x)$x)[1]) . You don't need to do this later because it's already matched up with its own odd x values. Scale 1) for the bin width of hist() and 2) for the frequency of x length(x), as DWin says. The last axis tick became visible after setting the xlim argument.
To do your problem 2, set up a plot with the correct dimensions (xlim and ylim), with type = "n", then draw 3 lines for the densities, scaled using something similar to the density line above. Think however about whether you want those semi continuous lines to reflect the heights of imaginary bars with bin width 5... You see how that might make the density lines exaggerate the counts at any particular point?
Although this is an aged thread, if anyone catches this. I would only think it is a 'good idea' to forego translating the y density to count scales based on what the user is attempting to do.
There are perfectly good reasons for using frequency as the y value. One idea in particular that comes to mind is that using counts for the y scale value can give an analyst a good idea about where to begin the 'data hunt' for stratifying heterogenous data, if a mixed distribution model cannot soundly or intuitively be applied.
In practice, overlaying a density estimate over the observed histogram can be very useful in data quality checks. For example, in the above, if I were looking at the above graphic as a single source of data with the assumption that it describes "1 thing" and I wish to model this as "1 thing", I have an issue. That is, I have heterogeneous data which may require some level of stratification. The density overlay then becomes a simple visual tool for detecting heterogeneity (apart from using log transformations to smooth between-interval variation), and a direction (locations of the mixed distributions) for stratifying the data.
I'd like to use ggplot2 density geometry using a log transformation for the x scale:
qplot(rating, data=movies, geom="density", log="x")
This, however, produces a chart with probabilities larger than 1. One solution that seems to work is to scale the dataset before calling qplot:
qplot(rating, data=transform(movies, rating=log(rating))
But then the x axis doesn't look nice. What is the correct way to handle this?
It seems that my question doesn't not, in fact, make sense. It seems that it is OK that probability densities are larger than one, as per [2]. What is important is that the integral over the entire space is equal to one [3].
This gives the right answer.
qplot(rating, y = ..scaled.., data=movies, geom="density", log="x")
stat_density produces new values, one of them is ..scaled.. which is the density scaled from 0 to 1.
HTH