Fixing the R error – aesthetics must be either length 1 or the same as the data

The “aesthetics must be either length 1 or the same as the data” error message can occur when you are using the geom_boxplot function that comes with the ggplot2 package. This occurs if you don’t include a proper number of colors in the “fill” parameter for your plot. A common and annoying miss for tired r users.

Fixing this error comes down to matching up the r aesthetics vector with your data frame specifications. This aligns your colour choices (from the aesthetic mapping) with the different columns in the data frame to match up your data visualization with the data.

Description of the error

Here is an example of code that produces this error message, along with the results that you get when you run it.

> library(ggplot2)
> ggplot(data = airquality, aes(x=as.character(Month), y=Temp)) +
+ geom_boxplot(fill=c(‘red’, ‘yellow’))
Error: Aesthetics must be either length 1 or the same as the data (5): fill
Run `rlang::last_error()` to see where the error occurred.

if you look closely at the error message you will see that it gives a clue as to how to fix it. It shows that you need to have either one color or the number of colors needs to be the same as the number of values in the x column. In this case that would be the number of months that the data set uses, it even indicated that the value is five.

Explanation of the error

Explaining this error requires looking at the data set. Simply supplying the name of the data set will result in a complete list of the data. To keep it from being too long, in the following example, I only included the first day of each month.

> airquality
Ozone Solar.R Wind Temp Month Day
1 41 190 7.4 67 5 1
32 NA 286 8.6 78 6 1
62 135 269 4.1 84 7 1
93 39 83 6.9 81 8 1
124 96 167 6.9 91 9 1

As you can tell from this truncated version of the airquality data set it uses exactly five months, that being May through September, as indicated by numbers five through nine. If you set the fill parameter to only one color, it knows to use that color for all five months. If you give the fill parameter five colors it knows to use one color for each month. However, if you give the fill parameter any other number of colors the function does not know how to distribute them to the boxplots resulting in our error message.

How to fix this error: method one.

Here we have an example code for the first method of fixing this error message. It is a simple matter of eliminating the second color and reducing the size of the fill parameter to one.

> library(ggplot2)
> ggplot(data = airquality, aes(x=as.character(Month), y=Temp)) +
+ geom_boxplot(fill=c(‘red’))

When you run this code, R studio produces a boxplot graph consisting of five red boxplots. In this situation we fixed the error message by reducing the number of colors to the minimum of one, making all of the boxplots the same color. This is the simplest of the two methods of fixing this error message, but it has the disadvantage of also being the graph a little bland because you only have one color. If you are looking for a quick fix for this error message and the colors are not important, this is the method you want to use.

How to fix this error, method two

If having each of the boxplots in your boxplot graph a different color is important or even helpful you may want to use this second method. It is a little more complicated than the first method because you need to make sure that you have the right number of colors in the vector of the fill parameter of the geom_boxplot function. This is done by making sure that the number of colors equals the number of boxplots in the boxplot graph. Here is some example code that shows how this works.

> library(ggplot2)
> ggplot(data = airquality, aes(x=as.character(Month), y=Temp)) +
+ geom_boxplot(fill=c(‘red’, ‘green’, ‘purple’, ‘orange’, ‘yellow’))

When you run this code, R studio will produce a graph of five boxplots with the colors red, green, purple, orange, and yellow. If you make a mistake on the number of colors, you will simply get our error message again, and all you need to do is add or remove colors until you get it right. If for some reason you want two of the boxplots to have the same color, all you need to do is duplicate the same color in the proper positions in the fill parameter.

This is an easy error message to get when working with boxplots because all you need to do is miscalculate the number of boxplots your graph is going to produce. Fortunately, it is an easy problem to fix because you have two options on how to do it. The first one is to make all of the boxplots the same color by giving the fill parameter only a single color. The second involves making sure that you give the fill parameter the same number of colors as the number of boxplots in your graph. The one to use depends upon how important the colors are to the graph making sense or just looking right.

The same approach works for other graphs (box plot, bar chart) supported by the ggplot2 package. You have a lot of creative freedom over the linetype, fill color, different layers, different columns of a ggplot2 plot. In addition to the usual label and axis elements (eg. y axis and x axis labels scale and design).

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