My hist function is not doing plots in R, what can i do?

Question

my My hist function is not doing plots in R, what can i do? This is an example of the data:

b=c(34,34,34,5,6,9,0,10,22,23)
t=hist(b)
t

and the output is:

$breaks
[1]  0  5 10 15 20 25 30 35
$counts
[1] 2 3 0 0 2 0 3
$density
[1] 0.04 0.06 0.00 0.00 0.04 0.00 0.06
$mids
[1]  2.5  7.5 12.5 17.5 22.5 27.5 32.5
$xname
[1] "b"
$equidist
[1] TRUE
attr(,"class")
[1] "histogram"

What can I do? thanks.

Answer 1

General considerations

The hist function in your case does exactly what it supposed to do. This function is used mainly for it's sideffect i.e. plotting the histogram (when argument plot is TRUE which is the default). But the value function returns is a list with several components (breaks, counts, density, mids, xname, equidist). So when you call t = hist(b) you assign the value returned by hist function, to the variable t (btw t is the function in R, I wouldn't use t as a variable name). As a result, when you cal t it prints returned value, a list mentioned above, but not a plot which you probably expect to see.

Getting your hands dirty (update)

Assuming that your objective is to save a histogram and plot it latter, you can use following observations:

Reproducible data

First we create a reproducible example:

set.seed(72158867)

x <- rnorm(100)

Here we assigned 100 random values to the variable x.

Create histogram, without plotting, assign the result to the variable

Now we are ready to create a histogram, and assign the result returned by hist() to the variable h:

h <- hist(x, plot = FALSE)

Here, with the argument plot = FALSE we tell the function to return result without plotting.

Inspect the content of h

The value returned by hist() is an object. We can dig into this object, to find how to work with it in order to achieve our objectives.

Structure of the returned object

First we can examine the structure of the returned object using the str() function:

str(h)

# List of 6
# $ breaks  : num [1:11] -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 ...
# $ counts  : int [1:10] 5 8 15 20 17 14 14 5 1 1
# $ density : num [1:10] 0.1 0.16 0.3 0.4 0.34 0.28 0.28 0.1 0.02 0.02
# $ mids    : num [1:10] -1.75 -1.25 -0.75 -0.25 0.25 0.75 1.25 1.75 2.25 2.75
# $ xname   : chr "x"
# $ equidist: logi TRUE
# - attr(*, "class")= chr "histogram"

Here we can see that the object returned by hist() is a list-like structure, with several elements. We can also see that the result hist() returned is a object of a class histogram.

Class of the returned object

Another way to identify the class of the object returned by hist() is calling a class() function on it.

class(h)

#[1] "histogram"

You can also call ?hist from your console, and find the information about returned value for the hist().

Methods defined on the returned object

To find out what kind of methods are defined on the object of class histogram we can use methods() function, as shown in example below:

methods(class = class(h))

# [1] lines plot 
# see '?methods' for accessing help and source code

Now we know that object of class histogram accepts two methods lines and plot. We are not interested in first one (however I wonder what it does), but second one seems to be something we are looking for.

Call plot method on the returned object

Let's call the plot() function on a histogram object:

plot(h, col = 'skyblue', border = 'yellow', main = 'Histogram for SOq #72158867')

It works as expected!

Basically, it is what hist() function does when you call it:

• It creates an object of class histogram from your data;
• It call plot method on your histogram object;
• It invisibly returns a resulting histogram object.

Of course there is a shorter way to find it out. Just type ?hist in your console, and you will find all hist-related information by yourself.