Skip to content Skip to sidebar Skip to footer

A Continuous Variable Can Not Be Mapped to Shape

Introduction

The ggplot2 package is a relatively novel arroyo to generating highly informative publication-quality graphics. The "gg" stands for "Grammar of Graphics". In short, instead of thinking about a unmarried function that produces a plot, ggplot2 uses a "grammar" approach, akin to building more and more complex sentences to layer on more information or nuance.

Data Model

The ggplot2 package assumes that data are in the form of a information.frame. In some cases, the data will need to be manipulated into a form that matches assumptions that ggplot2 uses. In detail, if i has a matrix of numbers associated with unlike subjects (samples, people, etc.), the information will usually need to be transformed into a "long" data frame.

Getting started

To use the ggplot2 package, it must be installed and loaded. Assuming that installation has been done already, we tin load the package direct:

            library(ggplot2)          

Playing with ggplot2

mtcars data

We are going to use the mtcars dataset, included with R, to experiment with ggplot2.

              data(mtcars)            
  • Exercise: Explore the mtcars dataset using View, summary, dim, course, etc.

We tin can also take a quick look at the relationships between the variables using the pairs plotting function.

              pairs(mtcars)            

That is a useful view of the information. We want to employ ggplot2 to make an informative plot, then let'due south approach this in a piecewise fashion. Nosotros get-go need to determine what type of plot to produce and what our basic variables will be. In this case, we have a number of choices.

              ggplot(mtcars,aes(x=disp,y=hp))            

First, a little explanation is necessary. The ggplot function takes as its first argument a information.frame. The 2d argument is the "aesthetic", aes. The ten and y take column names from the mtcars data.frame and will form the footing of our scatter plot.

But why did we get that "Error: No layers in plot"? Remember that ggplot2 is a "grammar of graphics". We supplied a subject, but no verb (chosen a layer by ggplot2). So, to generate a plot, nosotros demand to supply a verb. At that place are many possibilities. Each "verb" or layer typically starts with "geom" and and so a descriptor. An case is necessary.

              ggplot(mtcars,aes(x=disp,y=hp)) + geom_point()            

We finally produced a plot. The power of ggplot2, though, is the power to make very rich plots by calculation "grammar" to the "plot sentence". We have a number of other variables in our mtcars data.frame. How can we add another value to a two-dimensional plot?

              ggplot(mtcars,aes(x=disp,y=hp,color=cyl)) + geom_point()            

The color of the points is a based on the numeric variable wt, the weight of the motorcar. Tin we do more? We can change the size of the points, also.

              ggplot(mtcars,aes(x=disp,y=hp,color=wt,size=mpg)) + geom_point()            

And then, on our 2D plot, nosotros are at present plotting 4 variables. Can we practice more? We can dispense the shape of the points in addition to the color and the size.

              ggplot(mtcars,aes(x=disp,y=hp)) + geom_point(aes(size=mpg,color=wt,shape=cyl))            

Why did we get that error? Ggplot2 is trying to be helpful by telling us that a "continuous varialbe cannot exist mapped to 'shape'". Well, in our mtcars data.frame, we can look at cyl in detail.

              class(mtcars$cyl)            
              ## [1] "numeric"            
              summary(mtcars$cyl)            
              ##    Min. 1st Qu.  Median    Mean 3rd Qu.    Max.  ##   4.000   4.000   6.000   vi.188   8.000   8.000            
              table(mtcars$cyl)            
              ##  ##  4  vi  8  ## 11  7 xiv            

The cyl variable is "kinda" continuous in that it is numeric, but it could also be idea of as a "category" of engines. R has a specific data type for "category" information, called a factor. We can easily convert the cyl column to a factor similar then:

              mtcars$cyl = every bit.cistron(mtcars$cyl)            

Now, we can become ahead with our previous approach to make a 2-dimensional plot that displays the relationships between five variables.

              ggplot(mtcars,aes(x=disp,y=hp)) + geom_point(aes(size=mpg,colour=wt,shape=cyl))            

NYC Flight data

I leave this department open-ended for you lot to explore further options with the ggplot2 package. The data represent the on-fourth dimension information for all flights that departed New York City in 2013.

              library(nycflights13) head(flights)            
              ## # A tibble: six × 19 ##    year calendar month   day dep_time sched_dep_time dep_delay arr_time ##   <int> <int> <int>    <int>          <int>     <dbl>    <int> ## ane  2013     1     i      517            515         two      830 ## 2  2013     1     i      533            529         four      850 ## 3  2013     1     1      542            540         2      923 ## 4  2013     1     1      544            545        -i     1004 ## five  2013     1     1      554            600        -6      812 ## half-dozen  2013     1     1      554            558        -four      740 ## # ... with 12 more variables: sched_arr_time <int>, arr_delay <dbl>, ## #   carrier <chr>, flight <int>, tailnum <chr>, origin <chr>, dest <chr>, ## #   air_time <dbl>, distance <dbl>, hour <dbl>, infinitesimal <dbl>, ## #   time_hour <dttm>            

Experience gratis to explore. Consider using other "geoms" during your exploration.

Session Info

            sessionInfo()          
            ## R Nether development (unstable) (2016-10-26 r71594) ## Platform: x86_64-apple-darwin13.4.0 (64-bit) ## Running under: macOS Sierra 10.12.1 ##  ## locale: ## [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8 ##  ## attached base packages: ## [1] stats     graphics  grDevices utils     datasets  base      ##  ## other attached packages: ## [1] nycflights13_0.2.0 ggplot2_2.2.0      BiocStyle_2.three.15   ## [4] knitr_1.15.one       ##  ## loaded via a namespace (and non attached): ##  [1] Rcpp_0.12.8.2      codetools_0.2-15   assertthat_0.1     ##  [iv] digest_0.6.10      rprojroot_1.1      plyr_1.8.4         ##  [vii] grid_3.4.0         gtable_0.2.0       backports_1.0.4    ## [10] magrittr_1.5       evaluate_0.10      scales_0.4.1       ## [13] stringi_1.1.2      lazyeval_0.2.0     rmarkdown_1.2.9000 ## [16] labeling_0.3       tools_3.iv.0        stringr_1.one.0      ## [19] munsell_0.4.3      yaml_2.one.14        colorspace_1.3-1   ## [22] htmltools_0.3.five    tibble_1.2         methods_3.four.0          

rozekgress1990.blogspot.com

Source: https://seandavi.github.io/hour_of_code/ggplot2.html

Post a Comment for "A Continuous Variable Can Not Be Mapped to Shape"