Introduction
R programming language is becoming highly popular these days and is heavily used in machine learning and data science projects. I have been learning data science from an online course at Coursera, and they have used an amazing R package named swirl() to introduce various concepts of R. Here are the comprehensive notes of the same.
Here I assume, that the reader has basic knowledge of programming, since I do not dive deep in the grassroot level of explanation like variables, functions, etc. Basic knowledge of any programming language would be sufficient to get hold of following material. I have used command line R for executing following scripts, however even R Studio can be used.
Basic Building Blocks
> 5 + 7
[1] 12
# Assignment can be done with <-
x <- 5 + 7
> x
[1] 12
# Creating a simple vector in R
> z <- c(1.1, 9, 3.14)
> z
[1] 1.10 9.00 3.14
# See the function docs with ? , note do not add paranthesis
> ?c # Not ?c()
# Vectors can be concatenated in following way
> c(z, 555, z)
> c(z, 555, z)
[1] 1.10 9.00 3.14 555.00 1.10 9.00 3.14
# Can do arithmatic operations on vectors
> z*2 + 100
[1] 102.20 118.00 106.28 1210.00 102.20 118.00 106.28
# Can be squared using ^2, also sqrt() and abs() are some of the functions
# When given two vectors of the same length, R simply performs the specified arithmetic operation (`+`, `-`, `*`, etc.) element-by-element. If the vectors are of different lengths, R 'recycles' the shorter vector until it is the same length as the longer vector.
> c(1, 2, 3, 4) + c(0, 10)
[1] 1 12 3 14
> c(1,2,3,4) + c(0,10,100)
[1] 1 12 103 4
Warning message:
In c(1, 2, 3, 4) + c(0, 10, 100) :
longer object length is not a multiple of shorter object length
Workspaces in R
# Get current directory
> getwd()
[1] "/home/<your-complete-path>"
# List all objects of your current workspace
> ls()
character(0)
# Listing all files in current directory
> list.files() # Even dir() can be used
[1] "Rswirl.md"
# To see what arguments does a function take
> args(list.files)
function (path = ".", pattern = NULL, all.files = FALSE, full.names = FALSE,
recursive = FALSE, ignore.case = FALSE, include.dirs = FALSE,
no.. = FALSE)
# To create directory
> dir.create('testdir')
# To change the directory
> setwd('testdir')
# Create a file using
> file.create('mytest.R')
[1] TRUE
# Check whether file exists using
> file.exists("mytest.R")
[1] TRUE
# Check some information about the file using file.info(file)
# Rename file using file.rename(old, new)
# Delete using file.remove(file)
# Copy using file.copy(file, copy)
# Can use file.path()
> file.path('folder1','folder2')
[1] "folder1/folder2"
# For creating nested directories, use recursive flag
> dir.create(file.path('testdir2','testdir3'), recursive = TRUE)
Sequences of Numbers
> 1:20
[1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
# Increments by 1, includes limits, doesn't exceed them
> pi:10
[1] 3.141593 4.141593 5.141593 6.141593 7.141593 8.141593 9.141593
> 15:1
[1] 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
> ?`:` # Gives documentation of operator :
> seq(1, 20) # Same as 1:20
> seq(0,10,by=0.5)
[1] 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
[16] 7.5 8.0 8.5 9.0 9.5 10.0
# If we don't care about the increment, but the length of numbers created
> seq(5, 10, length = 30)
# Get length using length(vector)
> seq(along.with = my_seq) # Same as 1:length(my_seq)
[1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
[26] 26 27 28 29 30
# Shorter version of above
> seq_along(my_seq)
[1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
[26] 26 27 28 29 30
# Use built-in functions whenever possible
> rep(0, times = 40)
[1] 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
[39] 0 0
> rep(c(0,1,2), times = 10)
[1] 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2
> rep(c(0,1,2), each= 10)
[1] 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2
I hope that was helpful, comment below for hugs or bugs.
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