```
<- 1
x <- c(2, 3, 4, 1, 5)
y
#we expect this to return 4 -- the index of the value 1 in y
match(x, y)
```

`[1] 4`

Some uses of match() from base R

I’ve sort of rediscovered base R’s `match()`

function recently, so I figured I’d add a page here about it.

Per it’s documentation, match “returns a vector of the positions of (first) matches of its first argument in its second.”

So let’s illustrate this with the following data:

```
<- 1
x <- c(2, 3, 4, 1, 5)
y
#we expect this to return 4 -- the index of the value 1 in y
match(x, y)
```

`[1] 4`

And if x contains multiple elements, it does the same thing for each element:

```
<- 1:2
x
match(x, y)
```

`[1] 4 1`

And if y contains repeats of the same element, we still just get the first match:

```
<- c(y, 1)
y
match(x, y)
```

`[1] 4 1`

The cool thing for me here is what we can use this for replacements.

The following code:

- draws
`x`

, 100 samples (with replacement) from a uniform distribution 1:10; - determines
`k`

, the number of unique values in`x`

; - draws
`y`

, which is`k`

samples from`LETTERS`

(a vector containing all capital letters); - creates a new vector,
`x_replace`

that replaces each unique value in`x`

with a corresponding value of`y`

. If we truly wanted to replace`x`

, we would just assign this last result to back to`x`

```
set.seed(0408)
<- 100
n <- sample.int(10, size = n, replace = TRUE)
x <- length(unique(x))
k <- sample(LETTERS, k, replace = FALSE)
y
<- y[match(x, unique(x))] x_replace
```

And to show that this does what we think, let’s look at the first 10 values of `x`

:

`1:10] x[`

` [1] 10 9 9 8 7 1 1 5 5 3`

as well as the first 10 values of `x_replace`

:

`1:10] x_replace[`

` [1] "S" "W" "W" "L" "K" "U" "U" "E" "E" "C"`

and we can see that “S” corresponds to 10, “W” corresponds to 9, “U” corresponds to 1, etc.