CODEWITHSUNDEEP
rggplot2histogram
Massimo2013
Massimo2013

Reputation: 593

Histograms with variable size binwidth in ggplot2

I have the following data 

 dati <- read.table(text="
        class     num
    1     0.0   63530
    2     2.5   27061
    3     3.5   29938
    4     4.5   33076
    5     5.6   45759
    6     6.5   72794
    7     8.0  153177
    8    10.8  362124
    9    13.5  551051
    10   15.5  198634
  ")

And I want to produce a histogram with variable size bins, so that the area of each bar reflects the total numerosity (num) of each bin. I tried

bins <- c(0,4,8,11,16)
p <- ggplot(dati) +
  geom_histogram(aes(x=class,weight=num),breaks = bins)

however, this produces a histogram where the length of each bar is equal to total numerosity of each bin. Because bin widths are variable, areas are not proportional to numerosity. I could not solve this apparently easy problem within ggplot2. Can anyone help me?

Upvotes: 7

Views: 10037

Answers (2)

slizb
slizb

Reputation: 6170

It sounds to me like you asking for how to produce variable sized bar widths. If so, you just need to call the 'width' parameter in your ggplot aesthetics like this:

ggplot(data, aes(x = x, y = y, width = num))

this method is discussed more in the following question: Variable width bars in ggplot2 barplot in R

Upvotes: 1

Blue Magister
Blue Magister

Reputation: 13363

I think you are looking for a density plot - this closely related question has most of the answer. You call y = ..density.. in geom_histogram().

This works because stat_bin (recall geom_histogram() is geom_bar() + stat_bin(), and stat_bin() constructs a data frame with columns count and density. Thus calling y = ..density.. pulls the right column for density, whereas the default (counts) is as if you call y = ..count...

##OP's code
ggplot(dati) +  geom_histogram(aes(x=class, weight=num),
 breaks = bins)

Count Histogram

##new code (density plot)
ggplot(dati) +  geom_histogram( aes(x=class,y = ..density.., weight=num),
 breaks = bins, position = "identity")

Density Histogram

You can find some further examples in the online ggplot2 help page for geom_histogram().

Upvotes: 6

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