Exact number of bins in Histogram in R

The integer specified as argument for nclass is used as a suggestion:

the number is a suggestion only

An alternative solution is to cut your vector into a specified number of groups and plot the result:

plot(cut(data, breaks = 4))

Use the breaks argument:

hist(data, breaks=seq(0,80,l=6),
       freq=FALSE,col="orange",main="Histogram",
       xlab="x",ylab="f(x)",yaxs="i",xaxs="i")

Building on the answer from Rob Hyndman:

Maybe a more generic solution would be to make the breaks considering the minimun and maximun values of the data, and the number of breaks = number_of_bins+1.

hist(data,breaks=seq(min(data),max(data),l=number_of_bins+1), 
     freq=FALSE,col="orange",
     main="Histogram",xlab="x",ylab="f(x)",yaxs="i",xaxs="i")

I like to be quite accurate about my data points:

hist(data,breaks = seq(min(data),max(data),by=((max(data) - min(data))/(length(data)-1))))

This should automate the process with little manual input.