I will show some R traps here. The purpose of this page is not going to tell you how “crappy” R is. R is great indeed and also these kind of “traps” can happen in any other languages.

if(a<-5)

Assume you want make a condition to check if “**a is smaller than negative five**“, then do something. So you wrote

`if (a<-5)`

`{`

` sin(pi/3) } `

but R will check if you “**assign positive five to a**” since “<-” in R is an assignment operator. And of course this is always TRUE. As a result, R will always do the calculations within the condition.

Solutions: use a better coding style. i.e. always put a space between the operator (either assignment operators or relations operators) and values e.g.,

`if (a < -5)`

`{`

` `

`sin(pi/3)`

`}`

or use the parentheses if you want to make sure what you are ding.

`if (a<(-5))`

`{`

` `

`sin(pi/3)`

`}`

#### break a long line

When you want to break a long expression into several lines in R, you don’t have to put a special notation at end of each line and R will check if your expression has finished. This makes thing convenient but also brings troubles. Assume you have a very long expression and you want to break it into two lines, e.g.

`myvalue <- sin(pi/3) + cos(pi/3) + 2*sin(pi/3)*cos(pi/3)`

The result should be 2.232051.

But you wrote

`myvalue <- sin(pi/3) + cos(pi/3) + 2*sin(pi/3)*cos(pi/3)`

R will think you have finished the expression at the end of first line and started a new expression from the second line. You will find the result is 1.366025 since the second part is not included in at all.

**Solutions: **You can either put a pair of parentheses in your expression like this

`myvalue <- (sin(pi/3) + cos(pi/3) `

` + 2*sin(pi/3)*cos(pi/3))`

but too many parentheses make the code very hard to read. So you can do the trick that alway break the line after the arithmetic operators

`myvalue <- sin(pi/3) + cos(pi/3) `

`+ 2*sin(pi/3)*cos(pi/3)`

#### diag() function with a vector

As is described in R help document, using ‘diag(x)’ can have unexpected effects if ‘x’ is a vector could be of length one, like this example

`> diag(7.4)`

` [,1] [,2] [,3] [,4] [,5] [,6] [,7]`

`[1,] 1 0 0 0 0 0 0`

`[2,] 0 1 0 0 0 0 0`

`[3,] 0 0 1 0 0 0 0`

`[4,] 0 0 0 1 0 0 0`

`[5,] 0 0 0 0 1 0 0`

`[6,] 0 0 0 0 0 1 0`

`[7,] 0 0 0 0 0 0 1`

** Solutions: ** To avoid this, use “diag(x, nrow = length(x))” for consistent behavior **when “x” is a vector**

`> x = c(1,2,3)`

`> diag(x,length(x))`

` [,1] [,2] [,3]`

`[1,] 1 0 0`

`[2,] 0 2 0`

`[3,] 0 0 3`

`> x = 2.4`

`> diag(x,length(x))`

` [,1]`

`[1,] 2.4`

#### sample(x) when length of x is 1 and x is an integer

The first argument of sample function has some inconsistent behaviors when the length of x is 1 and x is an integer, see this example

`sample(x=3, n = 10, replace=TRUE) # same as sample(x=1:3, n = 10, replace=TRUE)`

If you want to* sample “3” ten times with replacement,* i.e. you obtain a vector of ten 3, you have to check that condition explicitly.