title: "Using Stringr for strings"

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```{r setup, include=FALSE}

Text are strings and the R package stringr and/ stringi are libraries to help deal with string data as part of data analysis.

Note:*Text string color is red and is not customizable, I tried to have another color while having a dark mode.*

```{r echo=TRUE, warning=FALSE, message=FALSE, include=TRUE}

Messy text

Will use fruits data and text strings.

Detection methods return Boolean array or index location

- `str_detect(string, pattern) `

- `str_detect(fruit, pattern = "a")`

- `str_detect(txt, pattern = "<h1>")`

- `str_starts(fruit, pattern = "ap" )`

More detection functions:

- `str_which()` finds the indexes of strings that contain match

- `str_locate()` locates the positions of pattern match

- `str_locate_all(fruit, pattern = "an")`

- `str_coount() `count the number of matches in string

- `str_count(fruit, pattern = "an")`

- `str_sub(string, start= , end= )` extract substrings from character vector

- `str_subset(string, pattern= )` returns only string in pattern match

- `str_extract()`/ `str_extract_all()` returns 1st match in string as a vector / returns all matches

- `str_match()` / `str_match_all()` return 1st pattern match as a matrix

- `str_length(string)` returns length (width) of entire strings

- `str_pad(string, width= , side= c('left','right','both') ')` add string apdding

- `str_trunc(string, width= , side= )` truncate a string

- `str_squish(string)` trim whitespace from each end

- `str_replace(string, pattern= ,replacement= )` / `str_replace_all()`

- `str_to_lower()` converts strings to lowercase

- `str_to_upper()` converts strings to uppercase

- `str_to_title()` convert strings to title case

- `str_c(string1, string2, sep= )` join multiple strings into single string

- `str_flatten(string, collapse= )` combines into a single string

- `str_dup(string, times= n)` repeat strings by **n** times

- `str_split_fixed(string, pattern= , n= )` /`str_split()` / `str_split_()`

- `str_glue()` create string from strings and {expressions}

- `str_glue_data()` use a dataframe/ list to create a string from strings and {expressions}

`str_view_all(fruit, pattern = "berry")` returns a page with highlight matches.

This section is **need to know** :

- regular expressions go in " "

- special characters, run `?"'"` in RStudio terminal for full list

- `\\` = `\`

- `\"` = "

- `\n` = new line

- use `writeLines("\\.")` to see what is viewed

To match a specific character, use `"\\{char}"` example `"\\!"`

- {char} = . ! ? ( ) `{` `}` `\n` `\t`

- `\d` (any digit)

- `\w` (any word character)

- need 4 backslashes for 1 back slash `\\\\`

Note that the '.' expression returns everything except for new line.

- `"[:digit:]"` matches digits

- `"[:letters:]"` matches letters

- `"[:lower:]"` matches lowercase letters

- `"[:upper:]"` matches uppercase letters

- `"[:alnum:]"` matches letters and numbers

- `"[:punct:]"` matches punctuation

- `"[:graph:]"` matches letters, numbers, punctuation

- `"[:space;]"` matches space characters

- `"[:blank:]"` matches space and tab (not new line)

Custom searches of strings

This is the specialized part

In the folder vector is a list of csv files, to extract each of them properly need to use special formatting. In the pattern `\\d{n}` d is for digit and there are 3 digits after results and 4 digits after that. This is useful when running a `purrr` function.