R Course

Plots

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Learn about devices, and the most well-known plots such as histograms, bar charts, pie charts, and box plots.


Almost all the plots' functions have these arguments

  • main = "title": plot title
  • xlab = "title x": x-axis title
  • ylab = "title y": y-axis title
  • xlim = lim: x's values goes up to lim
  • ylim = lim: y's values goes up to lim
  • col = 'color': set the color (ex: 'red' or red(1.0) in crayon)

Utilities

Before starting, you may use these functions to add some lines, ... to a plot

  • points: draw points
  • line: draw points
  • abline : draw a line $y=ax+b$ (you may use h=x or v=y)
  • legend: add a legend
  • title: add a title
  • others: rect, segments, polygon, box, grid

You may add a background or save some settings before drawing using par function like par(bg="...").


Devices

Sometimes you may want to export a plot (without using Rmd). You can do that by changing the device. Create a device with

  • pdf(path) (PDF)
  • jpeg(path) (JPG)
  • png(path) (PNG)

Then you should get a number, keep it in mind. Every plot will be rendered in the device you opened. Then use dev.off() or dev.off(number) to close the device. You should be able to open/see the resulting file. You can also use dev.copy(device=format, "path").


Plot

  • French: Diagramme de points
  • Function: plot(x)

If you have more than one point at a position, you won't see it using plot, so you will have to use plot(jitter(x)) to move the points a bit before rendering them.

You may use the argument type to change the type of plot, like type = "l" (l=line, b=line with dots).


Histogram

  • French: Histogramme
  • Function: hist(x)

New arguments

  • border = color
  • breaks = seq(...): make more columns, smaller intervals
  • nclass = v: make $v$ intervals

Notes

We are adding the argument prob = TRUE sometimes in statistics to make a histogram of the frequencies instead of the quantities.


Bar chart

  • French: Diagramme en batons/barres
  • Function: barplot(table(qual))

Let's say you got a qualitative variable (a variable taking finite values like Men/Women/Other) then you can see using this graph how many persons are taking each value.


Pie chart

  • French: Camembert
  • Function: pie(table(qual))

Same as Bar chart, but represented using the traditional pie chart.


Box plot

  • French: Boite à moustache
  • Function: boxplot(???)

My favorite one. You can

  • see the distribution (quantiles, ...) of a variable (boxplot(x))
  • ... by a criterion (boxplot(quant ~ qual))
data('mtcars'); cars <- mtcars
cars$cyl.qual <- factor(cars$cyl)
# you will see for each value
# or cyl=the number of cylinders
# the repartition of
# hp=the horse power
boxplot(cars$hp ~ cars$cyl.qual)

https://cdn.jsdelivr.net/gh/lgs-games/memorize/maths/r/utils/images/boxplot.png

The highest bar is the 3rd quantile, the lowest one is the first quantile and the black bar is the median (2nd quantile).


???

  • French: Diagramme temporel/de températures
  • Function: plotmeans(quant~qual) (from gplots)

If you want to see the evolution of a quantitative variable with a temporal qualitative variable, then use this. The value at a time $t$ is the mean of the values observed at the time $t$.


???

  • French: Diagramme en fagot
  • Function: interaction.plot(qual, quant, quant, lty=1, legend=FALSE)

Same as the diagram above, but this time we are not taking the mean and representing all values.


Contingency table

  • French: Tableau de contingence
  • Function: balloonplot(table(x))

Remember, that table is making a contingency table. You can visualize a contingency table using balloonplot.


Pivot table

  • French: Tableaux croisés
  • Function: qhpvt(data, rows = ..., columns = ..., calculations = "...")
  • Library: pivottabler

You can observe the relation of a variable with other variables.

  • data: your data
  • rows: a vector of variables (i)
  • cols: a vector of variables (j)
  • calculation: the operation we will do on each (i,j)
    • mean() (mean)
    • n() (count)
    • ...
  • formats: cell format (ex: %.1f)
  • totals: totals line (totals='totals=NONE'=remove totals)