> For the complete documentation index, see [llms.txt](https://docs.bcbi.brown.edu/codiac-for-health/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.bcbi.brown.edu/codiac-for-health/computing/r/regular-expressions.md).

# Regular Expressions

## RegEx Functions

<table><thead><tr><th>Action</th><th>Function</th><th data-hidden></th></tr></thead><tbody><tr><td>Search for a substring within a string</td><td>grep(<strong>substring/value</strong>, <strong>string</strong>)</td><td></td></tr><tr><td>Replace a single value within a string</td><td>sub(<strong>pattern</strong>, <strong>replacement</strong>, <strong>string</strong>)</td><td></td></tr><tr><td>Replace all instances within a string</td><td>gsub(<strong>pattern</strong>, <strong>replacement</strong>, <strong>string</strong>)</td><td></td></tr><tr><td>Find matches for exact string</td><td>grepl(<strong>pattern</strong>, <strong>string</strong>)</td><td></td></tr></tbody></table>

#### Inputs:

```r
#Search for substring in a string
y <- c("carrot", "apple", "banana", "carrot")
grep("carrot", y)

#Replace a single value within a string
sub("r”, “R”, y)

#Replace all instances within a string
gsub(“r”, “R”, y)

#Find matches of exact strings
grepl("car", y)
```

#### Outputs:

```r
#Search for value in a string
1 4
#Returns the position of the value searched for

#Replace the first instance of a single value within a string
"caRrot" "apple" "banana" "caRrot" 

#Replace all instances within a string
"caRRot" "apple" "banana" "caRRot"

#Find matches of exact strings
TRUE FALSE FALSE TRUE
```

## Resources

* DataCamp: [Regular Expressions](https://www.rdocumentation.org/packages/base/versions/3.6.2/topics/grep)


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