Cheat Sheet Informatica 2 SI22
Utilities:
● getwd() : Find the current directory
● setwd(‘path’) : Change the working directory
● rm(x) : Remove x from the environment
● rm(list = ls()) : Remove all variables
Matrix:
● Create:
○ m <- matrix(x, nrow=3, ncol=3) : Creates a 3x3 matrix from x
○ rbind(x, y, z) : Bind rows
○ cbind(x, y, z) : Bind columns
● Access:
○ m[2, ] : Select a row
○ m[ ,1] : Select a column
○ m[2, 3] : Select an element
● Change:
○ m[rowldx, columnldx] <- 5.5 : Change one element
○ m <- m[ , -columnldx] : Delete one column
○ m <- c(m) : Convert to Vector
Matrix Calculus:
● Addition: A + B addition of matrices of same dimension
● Trace: matrix.trace(A)
● Multiplication:
○ Matrix: A %*% B
○ Scalar: a * B
○ (row) vector * matrix: a = general, b = column, c = row
c %*% B
○ Matrix * (column) vector: B %*% b
○ (inner) product of 2 vectors → scalar: a = general, b = column, c = row
c %*% b
○ (outer) product of 2 vectors → matrix: b %*% c
○ Element-by-element: C <- A * B
● Transpose: t(A)
● Row ↔ Column vector: a = general, b = column, c = row
b <- t(c), b <- t(t(b))
● Inverse Matrix: Check before if det not equal to 0, det(a) , then solve(A)
● Sum of a Vector: a = general, b = column, c = row
rep(1, length(b)) %*% b
● Sum of Squares: a = general, b = column, c = row
t(b) %*% b
c %*% t(c)
● Covariance Matrix: N <- 1000, X <- matrix
N <- dim(x)[1] number of observations
Xbar <- colMeans(X) vector of means
1/(N-1)*t(X) %*% X - outer(Xbar, Xbar)
● Rank: qr(X)$rank
Cheat Sheet Informatica 2 SI22
Plots:
Import/Install ggplot2 → library(ggplot2)/install.packages(ggplot2)
● Bar Chart:
○ Standard One:
ggplot(data = grade, aes(x = country)) + geom_bar() + ggtitle("Student origin")
+ xlab("Country of origin") + ylab("Number of students")
○ Horizontal One:
ggplot(data = grade, aes(x = country)) + geom_bar() + coord_flip()
● Pie Chart:
Bar Charts but with polar coordinates
emptyTheme <- theme(axis.text = element_blank(), axis.ticks = element_blank(),
panel.grid = element_blank())
ggplot(data = grade, aes(x = 1, fill = country)) + geom_bar() + coord_polar(theta =
"y") + emptyTheme + xlab("") + ylab("")
● Doughnut Charts:
ggplot(data = grade, aes(x = 0.75, fill = country)) + geom_bar(width=0.5) +
xlim(c(0,1)) + coord_polar(theta = "y")
● Scatter Plot:
ggplot(data = grade, aes(x = math, y = stat, color=gender, shape=country)) +
geom_point() + scale_color_manual(values=c("pink", "skyblue3")) +
scale_shape_manual(values=c(16, 3, 17)) + theme_minimal()
● Line Chart:
ggplot(data = economics, aes(x = date, y = unemploy)) + geom_line()
● Statistical Plots:
○ Boxplot: ggplot(data=grade, aes(x=gender, y=math)) + geom_boxplot() +
stat_boxplot(geom ='errorbar')
○ Histogram: ggplot(data=grade, aes(x=math, fill=gender)) +
geom_histogram(binwidth = 1, position = "dodge")
○ Density: ggplot(data=grade, aes(x=math, fill=gender)) +
geom_density(alpha=0.5)
○ Qqplot: ggplot(data=grade, aes(sample = econ))
+stat_qq(distribution=qnorm) + stat_qq_line()
