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Rust split ExamplesSeparate strings with the split method, using a function to test for delimiter chars.
Split. When processing text, we often need to separate apart the values in the strings. Parts are separated with delimiter chars or strings.
Iterator notes. When we invoke split() we get an iterator. This can be used in a for-loop, or it can be collected into a Vec of strings.
String Array
First example. To begin, we use split() in the simplest way possible. We first declare a string literal (test) that has a delimiter char—here it is a semicolon.
Step 1 We invoke split, passing the semicolon as an argument—it is a char argument. We do not convert or collect the iterator.
Step 2 We loop over the resulting iterator with the for-in loop. We print each value, getting the results of split as we proceed.
for
Rust program that calls split with character
fn main() { let test = "cat;bird"; // Step 1: get iterator from splitting on character. let values = test.split(';'); // Step 2: print all results from iterator. for v in values { println!("SPLIT: {}", v) } }
SPLIT: cat SPLIT: bird
Delimiter function. Suppose we wish to have more complex logic that tests for a delimiter. We can use a closure, or a function, to test chars.
Here We have 2 chars we want to split on, the space and newline chars. Whitespace_test returns true if the argument matches.
Rust program that calls split with function
fn whitespace_test(c: char) -> bool { return c == ' ' || c == '\n'; } fn main() { let test = "cat dog\nbird"; // Call split, using function to test separators. let values = test.split(whitespace_test); // Print results. for v in values { println!("SPLIT: {}", v) } }
SPLIT: cat SPLIT: dog SPLIT: bird
Split and parse. It is possible to split apart a string and parse each number in the string. This code is often used for parsing in text files containing numbers.
Info We split the string on spaces, and then parse each resulting string in the iterator with the parse() function.
parse
Rust program that uses split and parse
fn main() { let test = "123 456"; let values = test.split(' '); for v in values { // Parse each part. let parsed: u32 = v.parse().unwrap(); // Add 1 to show that we have a u32 value. println!("SPLIT PARSE: {} {}", parsed, parsed + 1) } }
SPLIT PARSE: 123 124 SPLIT PARSE: 456 457
Read file, split. Suppose we have a file of key-value pairs, with a key and value separated by an equal sign on each line. With Rust we can parse this file into a HashMap of string keys.
Start We open the file with File open() and then loop over the lines() in the file. Then we split() each line.
File
Collect We collect the result of split, and then place the left side as the key, and the right side as the value in the HashMap.
HashMap
Finally We get a key from the HashMap, which was populated by the file we just read in. The file text is shown in the example.
Rust program that reads and splits lines in file
use std::io::*; use std::fs::File; use std::collections::HashMap; fn main() { // Open file of key-value pairs. let file = File::open("/Users/sam/example.txt").unwrap(); let reader = BufReader::new(file); let mut hash: HashMap<String, String> = HashMap::new(); // Read and parse file. for line in reader.lines() { let line_inner = line.unwrap(); let values: Vec<&str> = line_inner.split('=').collect(); if values.len() == 2 { hash.insert(values[0].to_string(), values[1].to_string()); } } // Get value from file. let cat = hash.get("cat"); if let Some(value) = &cat { println!("VALUE FOUND: {}", value); } }
VALUE FOUND: orange
bird=blue cat=orange
Split once. Suppose we have a string and it has one separator, and we want to split apart the two sides of the string. This can be done with a split_once call.
And We can avoid complicated collect() method calls or loops. Just assign a tuple pair to the result of split_once.
Tip Many uses of split() can be replaced with split_once(), so it is a good function to know.
Rust program that separates line once
fn main() { let value = "left:right"; // Get left and right from value. let (left, right) = value.split_once(":").unwrap(); println!("left = {} right = {}", left, right); }
left = left right = right
A summary. Split() is often used with Vec and string arrays. We can pass functions (or closures) to split() for more complex behavior. An iterator is returned.
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