...Text strings

")` - `str_starts(fruit, pattern = "ap" )` ```{r} str_starts(text2, pattern = "//") ``` 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")` ```{r} str_which(fruit, pattern = "ma") ``` ### Subset strings - `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 ```{r} str_sub(text2, start = 4, end = 17) str_subset(fruit, pattern = "bl") str_extract_all(txt, "edit") ``` ### manage string lengths - `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 ```{r} str_length(txt) str_pad(fruit[1], width=15, side='left') # pad on left side of 1st element in fruits sentences[1] str_trunc(sentences[1], width = 17, side='right') str_squish(sentences[1]) ``` ### Mutate strings - `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 ```{r} str_replace(text2, pattern = "nEvEr", replacement = "always") str_to_lower(txt, locale = 'en') str_to_upper(txt) str_to_title(txt) ``` ### Join & Split strings - `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} ```{r} str_c(letters[1:5], LETTERS[1:5], sep = "^") str_c(txt, text4, sep = " :: ") str_flatten(fruit[1:5], collapse = " % ") str_dup(text3, times = 3) str_split_fixed(txt, pattern = "YOU", n= 3) str_glue("Pi is {pi}") str_glue(text2, text7) # starwars data is from dplyr str_glue_data(head(starwars), "starwars has {head(name)}") ``` ### Order Strings ```{r} str_order(letters[1:10], decreasing = F, numeric = T) str_sort(letters[10:1]) ``` ### Helpers `str_view_all(fruit, pattern = "berry")` returns a page with highlight matches. ```{r} # override existing encoding of letter str_conv(fruit[1:4], encoding = "ISO-8859-1") str_wrap(txt, width = 5, indent = 2, exdent = 3) str_wrap(letters, width = 5, indent = 7) ``` ## Regular Expressions (RegEx) 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 ### Match character 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. ### RegEx Helpers - `"[: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) ```{r} expressions = c("abc ABC 123\t!?\\(){}\n") str_extract_all(text7, "[:digit:]") str_extract_all(text2, "[:alnum:]") str_extract_all(text2, "[:lower:]") str_extract_all(text6, "[:alpha:]") ``` ### Alternates Custom searches of strings ```{r} # match A or B # str_match(fruit, "apple|pear") str_count(text3, "0|9") # match one of str_match_all(text3, "[09]") # match anything but str_extract_all(text6, "[^http://]") # match a string between a range str_extract_all(text4, "[Text - strings]") ``` ### Quantifiers ```{r} # match 0 or more str_match_all(txt, "edit?") str_match(folder, "2020?") # match ZERO or more str_match(text3, "8*") # match exactly n times str_match_all(text6, "w[2]") # match n or more times str_match_all(txt, "edit[2,]") # match between n and m times str_match_all(text3, "0[1,3]") ``` ### Anchors ! This is the specialized part ```{r} # match at start of string str_count(folder, "^results") # match at end of string str_detect(folder, ".csv$") ``` In the folder vector is a list of csv files, to extract each of them properly need to use special formatting. In the pattern `\\d{n}` d is for digit and there are 3 digits after results and 4 digits after that. This is useful when running a `purrr` function. ```{r} folder str_extract_all(folder, "^results-\\d{3}-\\d{4}.csv$") ``` ### Look arounds ```{r} s ="bacad" # match followed by a char str_match(s, "a(?=c)") # match not followed by a char str_extract_all(s, "a(?!c)") # match preceded by str_extract_all(s, "(?

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