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# Numeric Operators in R

#### Part of Mike's Big Data, Data Mining, and Analytics Tutorial

R provides a number of operators for performing mathematical operations on numbers and vectors. Unlike most other programming languages, R can seamlessly take objects of different forms (single numbers, vectors, arrays) and perform operations with them.

In the case when two inputs have different lengths, R will “recycle” elements from the shorter input by repeating the shorter input to get the correct length. This is best demonstrated by example:

```
a<-rep(1,10) # 1 1 1 1 1 1 1 1 1 1
b<-1:3 # 1 2 3
#b treated as# 1 2 3 1 2 3 1 2 3 1
#Note the warning...
a+b # 2 3 4 2 3 4 2 3 4 2
```

```
## Warning in a + b: longer object length is not a multiple of shorter object
## length
```

`## [1] 2 3 4 2 3 4 2 3 4 2`

In general, I think recycling elements makes understanding R code harder, and I would generally treat it as an antipattern in R (i.e. don’t do it…). In addition to making code harder to understand, it will also help you start a bad habit of ignoring errors and warnings in R. There are better methods (`rep`

,`expand.grid`

,`combn`

, etc) that preserve code readability if you (or someone else) needs to do any review/modification in the future.Like most other programming languages, R operators follow a precedence that is similar to the precidence taught to math students (i.e. parentheses first, then multiply/divide, then addition/subtraction). I will cover this section discussing the most common operators and precedence from high to low (see

`?Syntax`

for the full list).##
`^`

Exponentiation

An exponent can be defined as one number (the base) multiplied by itself a number of times (the exponent). Here `4`

is the exponent and `2`

is the base:\[ 2^4 = 2 \cdot 2 \cdot 2 \cdot 2 = 16 \]

In the case of a non-whole exponent, exponentiation works as an nth root operation. For example:

\[ 8^{\bar{.3}} = 8^{\frac{1}{3}} = \sqrt[3]{8^1} = \sqrt[3]{8} = 2 \]

Negative exponents work as division operations. For example:

\[ 2^{-3} = \frac{1}{2^3} = \frac {1}{8} = 0.125 \]

R accomplishes exponentiation via the

`^`

operator. A few examples:`2^3#Exponent of a single number`

`## [1] 8`

`(1:10)^2#Exponent over an entire vector`

`## [1] 1 4 9 16 25 36 49 64 81 100`

`c(4,9,16,25,36)^(1/2)#nth root operation`

`## [1] 2 3 4 5 6`

##
`*`

Multiplication and `/`

Division Operators

Multiplication can be defined as the repeated addition of a number. Example:\[ 5 * 3 = 5 + 5 + 5 = 15 \]

Division can be defined in terms of splitting a quantity (called the numerator) between a set of groups (denominator). Example: 20 split between 5 groups yields 4 for each of the 5 groups:

\[ 20 / 5 = 4 \]

Various rules exist and are taught in low level mathematics courses for finding multiplication and subtraction for non-whole numbers by hand.

R accomplishes multiplication with the

`*`

operator. A few examples:`2*2 #Multiplication of two numbers`

`## [1] 4`

`(1:5)*rep(2,5) #Multiplication of vectors`

`## [1] 2 4 6 8 10`

`c(1,2,3,4,5)*c(2,2,2,2,2) #Same as above`

`## [1] 2 4 6 8 10`

`(1:5)*2 #Multiplication of a vector by a number (all elements multiplied)`

`## [1] 2 4 6 8 10`

The vector example above illustrated (O are input, X are output):R accomplishes division with the

`/`

operator. A few examples:`4/2 #Division of two numbers`

`## [1] 2`

`seq(2,10,by=2)/rep(2,5)#Division of vectors`

`## [1] 1 2 3 4 5`

`c(2,4,6,8,10)/c(2,2,2,2,2) #Same as above`

`## [1] 1 2 3 4 5`

`seq(2,10,by=2)/2 #Division of a vector by a number (all elements divided by number)`

`## [1] 1 2 3 4 5`

The vector example above illustrated (O are input, X are output):The input objects need to be numeric to utilize numeric operators. An example is that lists can’t be multiplied/divided directly:

`list(x=2,y=3) * list(y=2,x=3) #Might yield list(x=6,y=6)? Nope...`

`## Error in list(x = 2, y = 3) * list(y = 2, x = 3): non-numeric argument to binary operator`

Matrix multiplication uses a different operator (`%*%`

). See the post on Matrix operations for more details.##
`+`

Addition and `-`

Subtraction Operators

Addition can be thought of as finding the magnitude of two combined quantities.\[ 1 + 1 = 2 \]

Subtraction can generally be thought of as finding the difference between two values.

\[ 2 - 1 = 1 \]

R accomplishes addition with the

`+`

operator. A few examples:`+5 #Unary addition operator - no change/effect`

`## [1] 5`

`2+10 #Addition of 2 numbers`

`## [1] 12`

`1:10+2 #Addition of number and vector`

`## [1] 3 4 5 6 7 8 9 10 11 12`

`1:10+11:20#Addition of 2 vectors`

`## [1] 12 14 16 18 20 22 24 26 28 30`

The vector example above illustrated (O are input, X are output):R accomplishes subtraction with the

`-`

operator. A few examples:`-5 #Unary negation operator - creates a negated quantity`

`## [1] -5`

`12-2 #Subtraction of 2 numbers`

`## [1] 10`

`3:12-2 #Subtraction of number and vector`

`## [1] 1 2 3 4 5 6 7 8 9 10`

`11:20-1:10#Subtraction of 2 vectors`

`## [1] 10 10 10 10 10 10 10 10 10 10`

The vector example above illustrated (O are input, X are output):R has more operators that will be considered in other posts.

- Matrix Operations in R
- Logical Operators in R
- Bitwise Operators in R

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