This repository is for studying R programming, based on the youtube channel Kee-Young Kwahk.
- how to create a vector: in a form of c()
c(1,2,3)
c('a','b','c')
c(TRUE,FALSE)- assign a value(vector) into a variable: use '=' or '<-'
vec1 = c(1,2,3)
vec2 <- c(TRUE,FALSE)- Using seq function to create a sequence
- seq(from=x, to=y): create a sequence starting from x to y by 1
- by=z: increment of z
- length.out: desired length of the sequence
- seq(from=x, to=y): create a sequence starting from x to y by 1
seq(from=0, to=6, by=2)
seq(from=1, to 2, length.out)- replicate value: rep()
- rep(x, times=3): repeat x 3 times
- each=y: repeat each element in the vector
- times=c(a,b,c): each element of x is repeated each value of the second vector in order separately
- length.out: desired length of the output vector
- rep(x, times=3): repeat x 3 times
rep(c(1,2,3), times=3)
rep(c(1,2,3), each=3)
rep(c(1,2,3), times=c(1,2,3))
rep(c(1,2,3), length.out=8)-
when combining numeric vector and character vector, the elements in the numeric vector is converted into a character vector
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str(): see the structure of the vector
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comma is used to represent the dimension of the vector
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length(): print the magnitude of the vector
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indexing: specifies element in the vector using brackets
vec2 = c(1,2,3)
vec2[1]- built-in vectors: LETTERS, letters, month.name, month.abb, pi
- Unlike other programming languages, R uses a vector calculation to calculate.
- in 1+2, 1 and 2 is a vector and + is a function
- vector calculation is performed in an element unit.
c(1, 2, 3) + c(4, 5, 6)- If two vectors are not in the same length, recycling rule applies.
- recycling rule: In a vector calculation of different length of vectors, R reuse the element of the shorter vector
c(1, 2, 3) + c(4, 5, 6, 7, 8, 9)- Warning message when the length of the longer vector is not a multiple of a shorter vector
c(1, 2, 3) + c(4, 5, 6, 7, 8)- logical operation
- ==, !=, <, >, <=, >=, !x, x|y, x&y, isTRUE()
- logical operation using vector calculation
x <- c(1,2,3,4,5)
y <- c(3,3,3,3,3)
x > y- same as comparing with scalar
x <- c(1,2,3,4,5)
x > 3- logical operator as a number
- TRUE: 1
- FALSE: 0
as.numeric(TRUE) TRUE*TRUE
- functions using logical vectors
- sum(): number of the elements that satisfy the condition
- any(): print TRUE if any element satisfies the condition
- all(): print TRUE if all elements satisfy the condition
y = c(0, 25, 50, 75, 100) sum(y>50) any(-3:3 > 0) all(-3:3 > 0)
- unique characteristic of ==
- floating point number: In some cases, the approximation of the real number is expressed using rounding, so even two equations representing the same number are expressed as not the same
- use all.equal() to ignore a slight difference
sqrt(2)^2 == 2 identical(sqrt(2)^2,2) all.equal(sqrt(2)^2,2)
- vector calculation with character vectors
- paste(): combine two character vectors like numeric vectors
- recycling rule also applies
fruit = c("apple", "banana", "strawberry") food = c("pie", "juice", "cake") paste(fruit, food) paste(fruit, "juice")
- paste(): combine two character vectors like numeric vectors
- R functions also use vectorized way to perform calculation
- absolute value
abs(-3:3)- logarithm
log(1:5)
log(1:5, base=exp(1))
log2(1:5)
log10(1:5)- factorial and combination
factorial(1:5)
choose(5, 2)- square root
sqrt(1:5)- significant value, default number is 7
options("digits")
signif(456.789, digits=2)
signif(456.789, digits=3)
signif(456.789, digits=4)- rounding
round(456.789, digits=2)
round(456.789)
round(sqrt(1:5),digits=2)
round(456.789, digits=-2)
round(11.5)
round(-5.5)
floor(456.78)
floor(-456.78)
ceiling(456.78)
ceiling(-456.78)
trunc(456.78)
trunc(-456.78)~ 14:50