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CT60A9710 Statistical mathematics/Lectures/sampleRcode.R

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+# A comment begins with #
+
+# Some useful keyboard shortcuts in R Studio:
+# CTRL+ENTER  Executes on the command line the script line containing the cursor
+# If you highlight / select text with mouse, CTRL+ENTER executes all the code
+# Same applies with => Run above
+
+
+# CTRL+1      Moves cursor to script window
+# CTRL+2      Moves cursor to command line
+# Up Arrow    [In console] Cycles through previously entered commands
+# TAB         Activates autocomplete - very useful for paths and variable names
+# F1          Searches help for the word containing the cursor
+
+
+
+##########################
+
+# Basic Math in R
+
+3 + 2
+4 - 6 #
+
+log(42 / 7.3)
+
+5 + 6 + 3 + 6 + 4 + 2 + 4 + 8 + 3 + 2 + 7
+7 + 3 - 5 * 2 # multiplication "5 * 2" is done before the additions and subtractions
+
+# Exponents
+exp(2) # e^2
+4^3
+4**3
+
+log(9, 3) # log to base 3 of 9
+sqrt(100) # square root of 100
+factorial(20)
+choose(10, 3) # binomial coefficient
+
+
+# R is flexible about numeric values - don't need to worry about integer vs. float
+2 / 3
+2.0 / 3.0
+
+# Expressions can be placed on a single line separated by semi-colons:
+2 + 3
+5 * 7
+3 - 7
+
+#########################
+# Storing values in variables
+a <- 2
+b <- 3
+a / b
+c <- 10.3
+
+# Variable names are case sensitive: y is not the same as Y.
+# Variable names cannot begin with numbers (e.g. 1x) or symbols (e.g. %x).
+# Variable names connot contain blank spaces (use back.pay not back_pay).
+
+##########################
+
+# Vector Math in R
+# We can use the c(...) command to create vectors from a list of values.
+
+prices <- c(5, 10, 12, 13)
+quantities <- c(100, 3, 2000, 40)
+
+# We reference entries by their location, given in square brackets.
+prices[2]
+
+# Some functions on vectors
+sum(prices)
+min(prices)
+max(prices)
+mean(quantities)
+
+# When vectors are of the same length, we can multiply them 'by index'
+prices * quantities
+
+
+##########################
+
+# From vectors, we can create data frames
+
+User_ID <- 1:8
+# Vector with values: 1 2 3 4 5 6 7 8
+
+Name <- c(
+    "John", "Lisa", "Susan", "Albert",
+    "Brian", "Emma", "David", "Alice"
+)
+
+# Note that you may break a vector in different lines without a problem
+
+gender <- c(
+    "Male", "Female", "Female", "Male",
+    "Male", "Female", "Male", "Female"
+)
+
+Points <- c(56, 76, 86, 96, 73, 87, 47, 98)
+
+Birth_year <- c(1994, 2001, 1980, 1999, 1972, 2004, 1965, 1984)
+
+# Now we can form a data frame
+df <- data.frame(User_ID, Name, gender, Birth_year)
+
+
+# Click "df" in the Environment pane
+
+# We can refer to columns of a frame by using $-symbol
+
+df$Name # All names
+
+# We can easily compute the age of the persons
+# This computes the age of every row:
+df$Age <- 2022 - df$Birth_year
+
+# Look df frame again, there is new column "age"
+View(df)
+# We can find the smallest age:
+min(df$Age)
+
+# Or maximum
+max(df$Age)
+
+# Or the average
+mean(df$Age)
+
+# One can use subset function to select a "subframe"
+
+young <- subset(df, Age < 30)
+
+###########################
+# Saving data to CSV
+### To check the default working directory, use "getwd()" without quotes.
+getwd()
+
+### To change the working directory, type the path in quotes inside
+### the setwd() command.
+
+### PC Example: setwd("C:/Users/YOURUSERNAMEHERE/Desktop/")
+
+# You can store data as
+write.csv(df, "example.csv")
+
+# Open your CSV in Excel, make some changes, save and close it
+
+###########################
+# Bringing data in from a CSV
+# Download the file "diamonds.csv" from Moodle
+# Store it to "Home > R_codes"
+# Click that file of Files pane
+# Select "Import Dataset"
+# After that RStudio install couple of packages
+# that are useful in importing data
+# After the packages are installed you can choose "import"
+# => You have a frame "diamonds".
+
+# Visualizing data
+plot(diamonds$carat, diamonds$price)
+
+# The first parameter is x-coordinate
+# The second parameter ix y-coordinate
+
+# For more information on plots, copy-paste the following address:
+# https://www.datamentor.io/r-programming/plot-function/