How do I superimpose a frequency polygon on top of a histogram in R using lines?

Question

I'm a beginner at R and RStudio and I'm trying to make a frequency polygon on top of a histogram using the "cars" dataset.

attach(cars)
hist(speed)
lines(speed, lwd=2, col = "royalblue")

What I need is the points coming properly on top of the histogram. I have seen this one using plots but I can't get to use it in my code.

Does this answer your question? [Fitting a density curve to a histogram in R](https://stackoverflow.com/questions/1497539/fitting-a-density-curve-to-a-histogram-in-r) — jay.sf, Jan 07 '20 at 18:16
@jay.sf It's close but the problem is that it's a density curve but I need a frequency polygon. [Here is what I hope to achieve](https://i.imgur.com/s6B7pcM.png) — Vaishnav Santhosh, Jan 07 '20 at 19:37
Welcome to Stackoverflow. Please, see here how to make a great reproducible R example: https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example — cmirian, Jan 07 '20 at 20:01
@VaishnavSanthosh Ah ok, didn't notice the difference, see answer. — jay.sf, Jan 07 '20 at 20:02

jay.sf · Accepted Answer · 2020-01-08T08:27:11.270

1

hist() has a hidden output which you can grab by assignment. Then feed lines() with it.

h <- hist(x, col=5)
lines(x=c(0, h$mids, tail(h$mids, 1) + el(diff(h$mids))), y=c(0, h$counts, 0), lwd=2)

Data:

set.seed(22522)
x <- rpois(50, 6)

edited Jan 08 '20 at 08:27

answered Jan 07 '20 at 20:01

jay.sf

This might be it but is there any way to mark the points on the middle of the bar [rather than than it shiftting to the left side?](https://i.imgur.com/XnMdVVi.png) – Vaishnav Santhosh Jan 08 '20 at 07:19
@VaishnavSanthosh Yes, I found already the `mids` in `h`, please see edit. – jay.sf Jan 08 '20 at 08:27
1

This is perfect! Thank you so much! – Vaishnav Santhosh Jan 08 '20 at 10:32

score 0 · Answer 2 · answered Jan 07 '20 at 20:03

0

Try

par(mfrow=c(2,2))
hist(speed)
lines(speed, lwd=2, col = "royalblue")

Alternatively, you can do it all at once in ggplot2. But I would need a data sample and your script.

Best

answered Jan 07 '20 at 20:03

cmirian

We haven't learnt ggplot2 so we can't use it. Also the data sample is the cars dataset. I have used attach(cars) for it. – Vaishnav Santhosh Jan 08 '20 at 04:30

2 Answers2