Simple String Patterns

This library makes it easier to match, split and extract strings in Rust. It builds on the Rust standard library. A parallel string-patterns crate provides extensions to work with regular expressions. Together, these crates aim to make working with strings as easy in Rust as it is Javascript or Python with cleaner syntax.

Simpler string matching methods such as starts_with, contains or ends_with will always perform better, especially when processing large data sets. Methods such as starts_with_ci and starts_with_ci_alphanum build on these core methods to facilitate string manipulation without regular expressions.

Version 0.3.0 sees a radical revision of the enums used to define string matching rules in the matched_by_rules(), matched_conditional(), filter_all_rules() and filter_any_rules() methods.

Simple Patterns versus Regular Expressions

The main advantages of simple-string-patterns lie in readability and miniminal overhead in lightweight applications that would not otherwise need regex support. Under the hood, regular expression engines compile regex syntax and convert them into more efficient string matching subroutines. Preliminary benchmarks show that rule sets with basic matching methods such as contains_ci perform better than their regex counterparts, but if you need to add multiple nested rules, a regex may be faster. The sibling regex-powered string-patterns crate makes this very easy. This crate is best suited to small utilities that need to process large quantities of strings with a range of highly predictable formats, e.g. in cryptography, logging.

Method overview

Simple case-insensitive match

let str_1 = "Dog food";
if str_1.starts_with_ci("dog") {
  println!("{} is dog-related", str_1);
}

Simple case-insensitive match on the alphanumeric characters only in a longer text

// This method is handy for validating text values from external data sources with
// inconsistent naming conventions, e.g. first-name, first_name, firstName or "first name"
let str_1 = "Do you spell hip-hop with a hyphen?";
if str_1.contains_ci_alphanum("hiphop") {
  println!("{} is hip-hop-related", str_1);
}

Filter a vector of strings by their first alphanumeric characters

// Methods ending in _alphanum are good for filtering strings that may have other
// to_strings() converts an array of &str references to a vector of strings
let sample_strs = [
  "/blue-sky.jpg",
  "----bluesky.png",
  "-B-l-u-e--sky",
  "Blueberry",
  " Blue sky thinking"
].to_strings();
let strings_starting_with_blue = sample_strs
  .into_iter()
  .filter(|s| s.starts_with_ci_alphanum("bluesky"))
  .collect::<Vec<String>>();
// should return all except "Blueberry"

Extract the third non-empty segment of a long path name

let path_string = "/var/www/mysite.com/web/uploads";
if let Some(domain) = path_string.to_segment("/", 2) {
  println!("The domain folder name is: {}", domain); // "mysite.com" is an owned string
}

Extract the head and tail or start and end from a longer string

let test_string = "long-list-of-technical-words"
let (head, tail) = test_string.to_head_tail("-");
println!("Head: {}, tail: {}", head, tail); // Head: long, tail: list-of-technical-words

let (start, end) = test_string.to_start_end("-");
println!("Start: {}, end: {}", start, end); // Start: long-list-of-technical, end: words

Capture an inner segment via multiple patterns

let source_str = "long/path/with-a-long-title/details";
  let target_str = "long";
  if let Some(inner_segment) = source_str.to_inner_segment(&[("/", 2), ("-", 2)]) { 
    println!("The inner segment between 'a' and 'title' is: '{}'", inner_segment); // should read 'long'
  }

Extract the first decimal value as an f64 from a longer string

const GBP_TO_EURO: f64 = 0.835;

let sample_str = "Price £12.50 each";
if let Some(price_gbp) = sample_str.to_first_number::<f64>() {
    let price_eur = price_gbp / GBP_TO_EURO;
    println!("The price in euros is {:.2}", price_eur);
}

Extract numeric sequences from phrases and convert them to a vector of floats

// extract European-style numbers with commas as decimal separators and points as thousand separators
let sample_str = "2.500 grammi di farina costa 9,90€ al supermercato.";
let numbers: Vec<f32> = sample_str.to_numbers_euro();
// If two valid numbers are matched assume the first is the weight
if numbers.len() > 1 {
  let weight_grams = numbers[0];
  let price_euros = numbers[1];
  let price_per_kg = price_euros / (weight_grams / 1000f32);
  // the price in kg should be 3.96
  println!("Flour costs €{:.2} per kilo", price_per_kg);
}

Split a string list of numbers into floats

// extract 64-bit floats from a comma-separated list
// numbers within each segment are evaluated separately
let sample_str = "34.2929,-93.701";
let numbers = sample_str.split_to_numbers::<f64>(",");
// should yield vec![34.2929,-93.701]; (Vec<f64>)

Match by all or any pattern rules without regular expressions

// Call .as_vec() at the end
let mixed_conditions = bounds_builder()
  .containing_ci("nepal")
  .ending_with_ci(".jpg");

let sample_name_1 = "picture-Nepal-1978.jpg";
let sample_name_1 = "edited_picture-Nepal-1978.psd";

// contains `nepal` and ends with .jpg
sample_name_1.match_all_rules(&mixed_conditions); // true

// contains `nepal` but does not end with .jpg
sample_name_2.match_all_rules(&mixed_conditions); // false

// contains `nepal` and/or .jpg
sample_name_1.match_any_rules(&mixed_conditions); // true

// contains `nepal` and/or .jpg
sample_name_2.match_any_rules(&mixed_conditions); // true

Filter by all pattern rules without regular expressions

// The same array may also be expressed via the new bounds_builder() function with chainable rules:
// You may call .as_vec() to convert to a vector of StringBounds rules as used by methods ending in _conditional
let mixed_conditions = bounds_builder()
  .containing_ci("nepal")
  .not_ending_with_ci(".psd");

let file_names = [
  "edited-img-Nepal-Feb-2003.psd",
  "image-Thailand-Mar-2003.jpg",
  "photo_Nepal_Jan-2005.jpg",
  "image-India-Mar-2003.jpg",
  "pic_nepal_Dec-2004.png"
];
/// The filter_all_rules() method accepts a *BoundsBuilder* object.
let nepal_source_files: Vec<&str> = file_names.filter_all_rules(&mixed_conditions);
// should yield two file names: ["photo_Nepal_Jan-2005.jpg", "pic_nepal_Dec-2004.png"]
// This will now return Vec<&str> or Vec<String> depending on the source string type.

Nested Rule Sets

As of verson 0.3.0 you may add nested rule sets with and / or logic. The former case is true only if all conditions are met, while the latter is true if any of the conditions are met. The BoundsBuilder struct now has a set of methods starting with and or or. You may call and(rules: BoundsBuilder) or or(rules: BoundsBuilder) directly with a nested rule set if you have a mix of rule types. However, if all rules have the same bounds, other methods accepting a simple array of patterns are available, e.g.

• or_starting_with_ci(patterns: &[&str])
• or_starting_with_ci_alphanum(patterns: &[&str])
• or_containing_ci(patterns: &[&str])
• or_ending_with_ci(patterns: &[&str])
• and_not_ending_with_ci(patterns: &[&str])

let filenames = [
  "my_rabbit_2019.webp",
  "my_CaT_2020.jpg",
  "neighbours_Dog_2021.gif",
  "daughters_Dog_2023.jpeg",
  "big cat.psd"
];

/// Match files containing the letter sequences "cat" or "dog" and ending in ".jpg" or ".jpeg";
let rules = bounds_builder()
  .or_contains_ci(&["cat", "dog"])
  .or_ends_with_ci(&[".jpg", ".jpeg"]);

let matched_files = filenames.filter_all_rules(&rules);
/// Should yield an array with "my_CaT_2020.jpg" and "daughters_Dog_2023.png"

The above example reproduces the following example regular expression /(cat|dog).*?.jpe?g$/. The _alphanum-suffixed variants let match only on numbers and letters within a string, i.e. ignorning any spaces or punctuation.

Filter by any pattern rules without regular expressions

// The same array may also be expressed via the new bounds_builder() function with chainable rules:
// Call .as_vec() at the end
let mixed_or_conditions = bounds_builder()
  .containing_ci("nepal")
  .containing_ci("india");

let file_names = &[
  "edited-img-Nepal-Feb-2003.psd",
  "image-Thailand-Mar-2003.jpg",
  "photo_Nepal_Jan-2005.jpg",
  "image-India-Mar-2003.jpg",
  "pic_nepal_Dec-2004.png"
];
  
let nepal_and_india_source_files: Vec<&str> = file_names.filter_any_rules(&mixed_or_conditions);
// should yield two file names: ["edited-img-Nepal-Feb-2003.psd", "photo_Nepal_Jan-2005.jpg", "image-India-Mar-2003.jpg", "pic_nepal_Dec-2004.png"]

// To combine and/or logic, you can filter all rules with a nested "or" clause.
let mixed_conditions_jpeg_only = bounds_builder()
  .ending_with_ci(".jpg")
  .or(mixed_or_conditions);
let nepal_and_india_source_files_jpgs: Vec<&str> = file_names.filter_all_rules(&mixed_conditions_jpeg_only);
// should yield two file names: ["photo_Nepal_Jan-2005.jpg", "image-India-Mar-2003.jpg"]

Enclose strings in common bounding characters

let sample_phrase = r#"LLM means "large language model""#;

let phrase_in_round_brackets = sample_phrase.parenthesize();
// yields (LLM means "large language model")
// but will not escape any parentheses in the source string.

let phrase_in_left_right_quotes = sample_phrase.enclose('“', '”');
// yields “LLM means "large language model"”
// in custom left and right quotation marks, but will not escape double quotes.

let phrase_in_double_quotes = sample_phrase.double_quotes_safe();
// yields “LLM means \"large language model\"" with backslash-escaped double quotes

Filter strings by character categories

let sample_str = "Products: $9.99 per unit, £19.50 each, €15 only. Zürich café cañon";

let vowels_only = sample_str.filter_by_type(CharType::Chars(&['a','e','i','o', 'u', 'é', 'ü', 'y']));
println!("{}", vowels_only);
// should print "oueuieaoyüiaéao"

let lower_case_letters_a_to_m_only = sample_str.filter_by_type(CharType::Range('a'..'n'));
println!("{}", lower_case_letters_a_to_m_only);
// should print  "dceieachlichcafca"

/// You can filter strings by multiple character categories
let sample_with_lower_case_chars_and_spaces = sample_str.filter_by_types(&[CharType::Lower, CharType::Spaces]);
println!("{}", sample_with_lower_case_chars_and_spaces);
// Should print "roducts  per unit  each  only ürich café cañon"

Strip spaces only

let sample_str = "19 May 2021 ";
let sample_without_spaces = sample_str.strip_spaces();
println!("{}", sample_without_spaces);
  // should print "19May2021";

Remove character categories from strings

let sample_without_punctuation = sample_str.strip_by_type(CharType::Punctuation);
println!("{}", sample_without_punctuation);
// should print "Products 999 per unit £1950 each €15 only Zürich café cañon";

let sample_without_spaces_and_punct = sample_str.strip_by_types(&[CharType::Spaces, CharType::Punctuation]);
println!("{}", sample_without_spaces_and_punct);
// should print "Products999perunit£1950each€15onlyZürichcafécañon";

Split a string on any of set of characters

let sample_str = "jazz-and-blues_music/section";
let parts = sample_str.split_on_any_char(&['-','_', '/']);
// should yield "jazz", "and", "blues", "music", "section" as a vector of strings

Traits

Enums

CaseMatchMode

Defines case-sensitivity and alphanumeric-only modes.

StringBounds

Defines simple match rules with the pattern and a positivty flag, e.g. StringBounds::Contains("report", true, CaseMatchMode::Insensitive) or StringBounds::EndsWith(".docx", CaseMatchMode::Insensitive). The bounds_builder method helps build these rule sets.

All options have pattern: &str, is_positive: bool and case match mode flags and acceot the same three arguments (&str, bool, CaseMatchMode) for the match pattern, positivity and case match mode.

CharType

Defines categories, sets or ranges of characters as well as single characters.

Structs

BoundsBuilder

This struct helps you build string pattern rules for use with the matched_by_rules(), filter_all_rules() and filter_any_rules() methods. The bounds_builder() function returns a base instance on which you may chain any number of rules and sub-rules.

Dev Notes

This crate serves as a building block for other crates as well as to supplement a future version of string-patterns. Some updates reflect minor editorial changes.

Version 0.3.13 introduces the .strip_spaces() method as shorthand for .strip_by_type(CharType::Spaces).

Version 0.3.11 introduces a .split_to_numbers::<T>(pattern: &str) method to split a string list of numbers into a vector of the specified number type. This is handy when parsing common input formats such as latitudes and longitudes represented as "42.282,-89.3938". This might fail via .to_numbers() when commas or points used as separators may be confused with decimal or thousand separators without other characters in between.

Version 0.3.8 New *and_not_+ rules methods

This version introduced a set of and_not_-prefixed rule methods to filter strings do not match the specified array of patterns, e.g. if we have a list image file names that start with animal names and we want to match those beginning with case-insensitive "cat" or "dog", but excluding those ending in "".psd" or ".pdf".

  /// file names starting with cat or dog, but not ending in .pdf or .psd
  let file_names = [
    "CAT-pic-912.png", // OK
    "dog-pic-234.psd",
    "dOg-photo-876.png", // OK
    "rabbit-pic-194.jpg",
    "cat-pic-787.pdf",
    "cats-image-873.webp", // OK
    "cat-pic-090.jpg", // OK
  ];

  let rules = bounds_builder()
    .or_starting_with_ci(&["cat", "dog"])
    .and_not_ending_with_ci(&[".psd", ".pdf"]);
  let matched_files = file_names.filter_all_rules(&rules);
  /// This should yield ["CAT-pic-912.png", "dOg-photo-876.png", "cats-image-873.webp", "cat-pic-090.jpg"]

Version 0.3.0 expands the range of rules available

This version introduced a radical revision to the StringBounds enum with supplementary BoundsPosition and CaseMatchMode enums, to handle the full range of rules available via bounds_builder(). These rule sets may be used with with the matched_by_rules(), filter_all_rules() and filter_any_rules().

Full documentation for the 0.2.* series is available in the Github repo in the v0-2 branch.

Version 0.2.5 introduces SimpleMatchAny and Whole matches in StringBounds.

This supplements SimpleMatchAll to apply or logic with rules sets (StringBound, tuples or simple strs). The StringBounds enum now has whole string match options (with case-insensitive and case-sensitive variants) to accommodate a mix of partial and whole string matches. It also adds a range of single-argument methods for bounds_builder().

Versions of the string-patterns crate before 0.3.0 contained many of these extensions. Since version 0.3.0 all traits, enums and methods defined in this simple-string-patterns have been removed. These crates supplement each other, but may be installed independently.

Version 0.2.2 introduces three new features:

• bounds_builder() makes it easier to define string matching rules methods requiring an array of StringBounds rules such as filter_all_conditional(). See example above.
• ToSegmentFromChars provides new methods to split on any of an array of characters, e.g. when processing common patterns that may use a predictable set of separators. This mimics characters classes in regular expressions and is more efficient when you only need to allow for a limited set of split characters.
• MatchOccurrences has a variant find_char_indices method that accepts a char rather than a &str. This avoids any need to cast a character to a string.