updated script d2

Scripts/day2_20240917.R

@@ -0,0 +1,174 @@
+# using character indices
+
+person <- c("January", "Weiner", 134)
+names(person) <- c("FirstName", "LastName", "Age")
+person[1]
+person["FirstName"]
+person["Age"]
+
+# converting to numbers
+
+person <- c(10, 20, "30")
+person
+person * 10
+person <- as.numeric(person)
+person
+person * 10
+
+person <- c("January", "Weiner", 134)
+as.numeric(person)
+
+measurement <- c(10, 20, "> 40", "N.d")
+as.numeric(measurement)
+
+## NULL value
+
+mynull <- NULL
+
+## logical vectors
+
+sel <- c(TRUE, FALSE, FALSE, TRUE, TRUE)
+sum(sel)
+!sel
+sum(!sel)
+
+samples <- c(1, 1, 2, 5, 7)
+samples >= 2
+sum(samples >= 2)
+sel <- which(samples >= 2)
+
+# this will return the same result as sum(samples >= 2)
+length(sel)
+samples[sel]
+samples[sel] <- 2
+samples
+
+persons <- c("Aphrodite", "Bacchus", "Circe", "Demeter", "Eurypides")
+sel     <- c(TRUE, TRUE, TRUE, TRUE, FALSE)
+persons[sel]
+
+# Exercise 2.1
+
+samples <- c(1, 10, NA, 15)
+mean(samples)
+NA + 5
+
+mean(samples, na.rm = TRUE)
+?mean
+which(is.na(samples))
+
+
+samples <- c(1, 10, NA, 15, NA)
+which(is.na(samples))
+sel <- !is.na(samples)
+samples[ sel ]
+samples[ !is.na(samples) ]
+
+areas <- c(0.1, 0.2, 0.4, 0.8, 1.6, 3.2)
+
+# the following are equivalent
+areas[ which(areas > 1)]
+areas[ areas > 1 ]
+
+# logical operations on logical vectors
+a <- c(1, 2, 3)
+b <- c(5, 6, 7)
+a + b
+
+a <- areas > 1 
+b <- areas < 0.3
+a | b
+a & b
+
+## rep and paste
+
+rep(c("A", "B"), 5)
+repvec <- rep(c("A", "B"), 5)
+length(repvec)
+rep(c("A", "B"), each=5)
+length(rep(c("A", "B"), each=5))
+
+paste("A", "B", "C")
+length(paste("A", "B", "C"))
+paste0("A", "B", "C")
+
+a <- c("A", "B", "C")
+b <- c("1", "2", "3")
+paste0(a, b)
+
+# exercise 2.1b
+a <- rep(c("A", "B", "C"), each = 3)
+b <- rep(1:3, 3)
+ab <- paste0(a, b)
+rep(ab, each = 3)
+
+
+# matrices
+
+m <- matrix(1:18, ncol=3, nrow=6)
+m <- matrix(0, ncol=3, nrow=6)
+View(m)
+
+# compare with
+m <- matrix(1:18, ncol=3, nrow=6, byrow=TRUE)
+
+# dimensions of the matrix; rows first, then columns
+dim(m)
+ncol(m)
+nrow(m)
+
+# all values in the first row
+m[ 1, ] 
+m[1,]
+
+# all values in the second column
+m[ , 2]
+
+# select more than one column
+m[ , 1:2]
+
+# same as simply m
+m[ , ]
+
+m[ 2, 3 ] <- 42
+m[ 1, ] <- pi
+
+# this converts the whole matrix to character values
+m[ 2, 3 ] <- "FORTY two"
+
+# this actually converts the matrix to a one dimensional vector
+as.numeric(m)
+
+# row and column names
+m <- matrix(1:18, ncol=3, nrow=6, byrow=TRUE)
+colnames(m) <- c("foo", "bar", "baz")
+m[ , "foo" ]
+m[ , 1 ]
+nrow(m)
+
+
+letters
+LETTERS
+
+rownames(m) <- letters[1:6]
+m[ "a", ]
+
+m[ 1, ]
+m[ "a", "foo" ]
+
+paste0(rep(letters, each = 26), rep(letters, 26))
+
+rownames(m) <- 2:7
+m[2, ]
+m["2", ]
+
+# use a prefix
+rownames(m) <- paste0("ID", 2:7)
+m[2, ]
+m["ID2", ]
+
+areas
+aeas
+
+# out of bonds
+m[ , 54 ]