R Notes
R is popular among statisticians and biologists. It is one of the most commonly used languages in data analysis.
Basics
R’s basic syntax is Clike. There are a few special usages compared to other languages:
<
is R’s way to express assign a value to a variable. It can also direct the other way, i.e.>
. Sometimes it is equivalent to=
, but in some places only<
is allowed. The recommended way is to use<
and forget that equals is ever allowed.<
is R’s global assigner. It can set global variables in a local scope.c()
is for combine scalars into vectors.list()
is for creating a collection with multiple object types (similar totuple
in other languages). R’s vectorization is similar to MATLAB, but not strictly consistent. If you attempt to use a nonvectorized function on a vector, you will get warnings.
apply()
is likemap()
in Julia. There are more functions in the apply family.  R uses onebased indexes (GREAT!).
 Integers in R are shown as e.g.
2L
.3
is assumed to be the same as3.0
, i.e.numeric
.  Terminating R expressions: R doesn’t need semicolons to end a line of code (while it’s possible to put multiple commands on a single line separated by semicolons, you don’t see that very often). Instead, R uses line breaks (i.e., new line characters) to determine when an expression has ended.
 Last but not least, R is a casesensitive language, consistent with the trend in most modern languages.
Popular Packages
ggplot2
: grammar of graphics. The most famous package in the R community.
library(ggplot2)
# Delete the points outside the limits
g + xlim(c(0, 0.1)) + ylim(c(0, 1000000))
ggplot(midwest, aes(x=area, y=poptotal)) +
geom_point(col="steelblue", size=3) + # Add scatter points
geom_smooth(method="lm") + # Add smoothing layer with a linear model "lm"
coord_cartesian(xlim=c(0,0.1), ylim=c(0, 1000000)) + # Zoom in
labs(title="Area Vs Population", subtitle="From midwest dataset", y="Population", x="Area", caption="Midwest Demographics") # Add titles and axis labels
tidyverse
: providing a complete and consistent set of tools for working with functions and vectors.
library(purrr)
mtcars >
split(mtcars$cyl) > # from base R
map(\(df) lm(mpg ~ wt, data = df)) >
map(summary) %>%
map_dbl("r.squared")
#> 4 6 8
#> 0.5086326 0.4645102 0.4229655
This example illustrates some of the advantages of purrr functions over the equivalents in base R:

The first argument is always the data, so purrr works naturally with the pipe.

All purrr functions are typestable. They always return the advertised output type (map() returns lists; map_dbl() returns double vectors), or they throw an error.

All
map()
functions accept functions (named, anonymous, and lambda), character vector (used to extract components by name), or numeric vectors (used to extract by position).
Advanced R
The tricks are moreorless similar to MATLAB and Python, such as vectorization, lazy evaluation, and integrating faster languages like C++. See more in Advanced R.