= Vectors =

'''Vectors''' are an ordered container [[R/DataTypes#Compositions|data type]].

<<TableOfContents>>

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== Instantiation ==

Vectors are commonly instantiated using the 'concatenation' function.

{{{
x <- c(1,2,3)
}}}

To instantiate a null [[R/DataTypes#Numeric|numeric]] vector of some size, try:

{{{
y <- double(length=100)
}}}

Note that `numeric` is an alias for the same `double` function.

To instantiate a null [[R/DataTypes#Character|character]] vector of some size, try:

{{{
z <- character(length=100)
}}}

Often there is a more appropriate default value than `""` however, so consider instead using:

{{{
z <- rep("foo", times = 100)
}}}

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== Accessing elements ==

Elements of a vector are accessed by indexing; note that vectors index from 1.

{{{
first <- x[1]
last <- x[length(x)]
second_and_third <- x[c(2,3)]
middle <- x[2:length(x)-1]
}}}

Assignment to elements works as expected.

{{{
x[2] <- 1
x[1] <- x[2]
x[c(2,3)] <- c(1,2)
}}}

Assigning to a non-existent element causes the vector to be extended as necessary, with null values at all indices between the 'old' last index and the 'new' last index.

Negative indexing causes the selected elements to be censored.

{{{
all_but_first <- x[-1]
all_but_second_and_third <- x[-c(2,3)]
}}}

Indexing by zero evaluates as an empty vector (i.e., length of 0) that is of the corresponding type.



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