Plot logistic regression curve in R

Question

I want to plot a logistic regression curve of my data, but whenever I try to my plot produces multiple curves. Here's a picture of my last attempt:

last attempt

Here's the relevant code I am using:

fit = glm(output ~ maxhr, data=heart, family=binomial)
predicted = predict(fit, newdata=heart, type="response")

 plot(output~maxhr, data=heart, col="red4")
 lines(heart$maxhr, predicted, col="green4", lwd=2)

My professor uses the following code, but when I try to run it I get an error on the last line saying that the x and y lengths do not match:

# fit logistic regression model
fit = glm(output ~ maxhr, data=heart, family=binomial)
# plot the result
hr = data.frame(maxhr=seq(80,200,10))
probs = predict(fit, newdata=dat, type="response")
plot(output ~ maxhr, data=heart, col="red4", xlab ="max HR", ylab="P(heart disease)")
lines(hr$maxhr, probs, col="green4", lwd=2)

Any help would be appreciated.

Edit:

As requested, reproduceable code using the mtcars dataset:

fit = glm(vs ~ hp, data=mtcars, family=binomial)
predicted= predict(fit, newdata=mtcars, type="response")
plot(vs~hp, data=mtcars, col="red4")
lines(mtcars$hp, predicted, col="green4", lwd=2)

Answer 1

The Code looks something like this:

fit = glm(vs ~ hp, data=mtcars, family=binomial)
newdat <- data.frame(hp=seq(min(mtcars$hp), max(mtcars$hp),len=100))
newdat$vs = predict(fit, newdata=newdat, type="response")
plot(vs~hp, data=mtcars, col="red4")
lines(vs ~ hp, newdat, col="green4", lwd=2)

​The Graph looks like this:

The predictions are made with the newdatobject. This dataset has a considerably better resolution of possible hpvalues than the original dataset, and it is organised to make charting easier. When you constructed hr, you were on your way to implementing it right, but you didn't use it in the prediction stage, instead using newdata=dat.

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