# Dangerous R functions and operators for programming

## Colon operator

The colon operator (`:`

) can be very dangerous when not used carefully. For example, you may use `1:length(x)`

, but what if the length of x is 0?

```
x <- c()
1:length(x)
```

`## [1] 1 0`

As you see, instead of a vector to match the length of x, you get a reversed vector of `c(1, 0)`

. It would be much better to use the `seq_along()`

function as follows:

```
x <- c()
seq_along(x)
```

`## integer(0)`

The related functions `seq()`

and `seq_len()`

are other related functions that should be used instead of the colon operator when used programmatically.

`sample()`

function

The `sample()`

function behaves differently whether it’s first input has length 1 or length greater than 1. This became a problem for me when I had a variable number of elements I needed to randomly select from.

Here we select a random element from a vector of length 3:

```
set.seed(1)
x <- c(2,5,7)
sample(x, size = 1)
```

`## [1] 2`

If x is chosen programmatically, then it may be of length 1.

```
set.seed(2)
x <- c(7)
sample(x, size = 1)
```

`## [1] 5`

See the problem? Instead of selecting the 7 like the previous example, it chose a random number from 1 to 7.

To get around this, I wrote a new function that has the behavior I was looking for:

```
sample_safe <- function(x, size, replace = FALSE, prob = NULL) {
if(length(x) == 1) {
return(x)
}
sample(x, size, replace, prob)
}
set.seed(1)
x <- c(2,5,7)
sample_safe(x, size = 1)
```

`## [1] 2`

```
set.seed(2)
x <- c(7)
sample_safe(x, size = 1)
```

`## [1] 7`

Now when `x`

is of length 1, only that element is returned.

## Other examples

Do you know any other examples? Let me know in the comments below and I may update this post or include them in a future post.