I need a histogram for my data, but could not find one with a curve. Can anyone please suggest a histogram showing frequencies (not densitities) with a curve for the data below? Fancy ones are preferred, but no worries if not :)
x <- rnorm(1000)
hist(x)
Here's the slow, step-by-step version.
This is your data.
population_mean <- 0
population_sd <- 1
n <- 1000
x <- rnorm(n, population_mean, population_sd)
These are some x coordinates for drawing a curve. Notice the use of qnorm to get lower and upper quantiles from a normal distribution.
population_x <- seq(
qnorm(0.001, population_mean, population_sd),
qnorm(0.999, population_mean, population_sd),
length.out = 1000
)
In order to convert from density to counts, we need to know the binwidth. This is easiest if we specify it ourselves.
binwidth <- 0.5
breaks <- seq(floor(min(x)), ceiling(max(x)), binwidth)
Here's our histogram.
hist(x, breaks)
The count curve is the normal density times the number of data points divided by the binwidth.
lines(
population_x,
n * dnorm(population_x, population_mean, population_sd) * binwidth,
col = "red"
)
Let's see that again with the sample distribution rather than the population distribution.
sample_mean <- mean(x)
sample_sd <- sd(x)
sample_x <- seq(
qnorm(0.001, sample_mean, sample_sd),
qnorm(0.999, sample_mean, sample_sd),
length.out = 1000
)
lines(
population_x,
n * dnorm(sample_x, sample_mean, sample_sd) * binwidth,
col = "blue"
)
Maybe something like this...?
set.seed(1)
x <- rnorm(1000)
hist(x, las=1)
par(new=TRUE)
plot(density(x), col=2, yaxt="n", xaxt="n",
bty='n', xlab="", ylab="", main='')
axis(4, las=1)
Frequency is depicted in the left y axis and Probability (for the density line) is in the right y axis.
Normally you would use a density curve.
Try this:
x <- rnorm(1000)
hist(x)
curve(dnorm, col = 2, add = TRUE)
