R 101: Vectors

Vectors are a basic data structure in R and are created using the c()
function. Unlike data frames and lists, the elements of a vector must be of
the same mode.

Functions can be used on a vector. For example, length(x) can be used to find the number of elements in x. Furthermore, conditions can be used to determine if the elements of a vector meet a certain criteria.

The elements of a vector can be selected by using the name of the vector
followed by an index vector in square brackets. Positive index values specify
the values to be included. Negative index values specifiy the values to be
excluded. Furthermore, vectors with a names attribute can be indexed using
its names.

# Creating vectors with the c() function
vecone <- c(1,3,5,7,9)
vectwo <- c(“KS”, “IA”, “NY”, “NY”, “FL”)
vecthree <- c(vecone, 0, vecone)

mode(vecone)
mode(vectwo)
mode(vecthree)

# Using functions on a vector
length(vecone)
length(vectwo)
length(vecthree)

max(vecone)
min(vecone)

# Vector arithmetic
vecone + vecone
vecone * 2
vecone^2

# Using conditions
vecon > 4
vecone > 4 & vecone < 9
vectwo == “KS”
vectwo != “KS”
vectwo[vectwo != “KS”]
which(vectwo != “KS”)
vectwo[c(2,3,4,5)]

# Indexing a vector
vecone
vectwo
vecone[1]
vectwo[1]
vecone[3]
vectwo[3]
vecone[1:3]
vectwo[1:3]
vecone[length(vecone)]
vectwo[length(vectwo)]

vecone[-2]
vectwo[-2]
vecone[-c(1:3)]
vectwo[-c(1:3)]
vecone[-length(vecone)]
vectwo[-length(vectwo)]

# Indexing a vector with names
newvec <- c(1,6,8,9,13,14)
names(newvec) <- c(“Var1″, “Var2″, “Var3″, “Var4″, “Var5″, “Var6″)
newvec
newvec[“Var3”]
newvec[c(“Var1”, “Var3”, “Var6”)]