The transformation of the function f(x) = 2x when it becomes f(x) = 2x-4 is a horizontal shift of 4 units to the left.

No it is actually a horizontal shift of 2 units to the right. 

The major difference is that a histogram is only used to plot the frequency of score occurrences in a continuous data set that has been divided into classes, called bins.  bar charts, on the other hand, can be used for a great deal of other types ofvariables  including  ordinal  andnominal  data sets.