How to eliminate up to n spaces at the beginning of each line?
For example, when trim 4 space:
" 5" ->" 5"
" 4" ->"4"
" 3" ->"3"
const INPUT:&str = " 4\n 2\n0\n\n 6\n";
const OUTPUT:&str = "4\n2\n0\n\n 6\n";
#[test]
fn main(){
assert_eq!(&trim_deindent(INPUT,4), OUTPUT)
}
I was about to comment textwrap::dedent, but then I noticed "2", which has less than 4 spaces. So you wanted it to keep removing spaces, if there is any up until 4.
Just writing a quick solution, it could look something like this:
Your assert will pass, but note that lines ending in \r\n will be converted to \n, as lines does not provide a way to differentiate between \n and \r\n.
fn trim_deindent(text: &str, max: usize) -> String {
let mut new_text = text
.lines()
.map(|line| {
let mut max = max;
line.chars()
// Skip while `c` is a whitespace and at most `max` spaces
.skip_while(|c| {
if max == 0 {
false
} else {
max -= 1;
c.is_whitespace()
}
})
.collect::<String>()
})
.collect::<Vec<_>>()
.join("\n");
// Did the original `text` end with a `\n` then add it again
if text.ends_with('\n') {
new_text.push('\n');
}
new_text
}
If you want to retain both \n and \r\n then you can go a more complex route of scanning through the string, and thus avoiding using lines.
fn trim_deindent(text: &str, max: usize) -> String {
let mut new_text = String::new();
let mut line_start = 0;
loop {
let mut max = max;
// Skip `max` spaces
let after_space = text[line_start..].chars().position(|c| {
// We can't use `is_whitespace` here, as that will skip past `\n` and `\r` as well
if (max == 0) || !is_horizontal_whitespace(c) {
true
} else {
max -= 1;
false
}
});
if let Some(after_space) = after_space {
let after_space = line_start + after_space;
let line = &text[after_space..];
// Find `\n` or use the line length (if it's the last line)
let end = line
.chars()
.position(|c| c == '\n')
.unwrap_or_else(|| line.len());
// Push the line (including the line ending) onto `new_text`
new_text.push_str(&line[..=end]);
line_start = after_space + end + 1;
} else {
break;
}
}
new_text
}
#[inline]
fn is_horizontal_whitespace(c: char) -> bool {
(c != '\r') && (c != '\n') && c.is_whitespace()
}
Related
I am trying to read a file into a string messages defined on line #14. The file contains several blocks where each block starts with a number. After I read the file contents into the string messahes, each block is separated by newline and each line in a block is separated by __SEP__. I would like to use par_split() on the string messages, process each block using rayon and collect output from each block into a vector vec_finale.g. by calling collect() on line 54 or some similar mechanism to produce a vector that contains vec_local on line 53 produced by each block. Any pointers on how I can achieve this are highly appreciated.
My code is as follows:
fn starts_with_digit_or_at_sign(inp: &str) -> bool {
let mut at_sign_found = false;
if inp.len() > 0 {
let ch = inp.chars().next().unwrap();
if ch.is_numeric() || ch == '#' {
return true;
}
}
return false;
}
fn main() {
let filepath = "inp.log";
let data = std::fs::read_to_string(filepath).expect("file not found!");
let mut messages: String = String::from("");
let separator_char = '\n';
let separator: String = String::from("__SEP__");
let mut found_first_message = false;
let mut start_of_new_msg = false;
let mut line_num = 0;
for line in data.lines() {
line_num += 1;
if line.len() > 0 {
if starts_with_digit_or_at_sign(line) {
start_of_new_msg = true;
if !found_first_message {
found_first_message = true;
} else {
messages.push(separator_char);
}
}
if found_first_message {
if !start_of_new_msg {
messages.push_str(&separator);
}
messages.push_str(line);
if start_of_new_msg {
start_of_new_msg = false;
let mut tmp = String::from("Lnumber ");
tmp.push_str(&line_num.to_string());
messages.push_str(&separator);
messages.push_str(&tmp);
}
}
}
}
messages.par_split(separator_char).for_each(|l| {
println!(
"line: '{}' len: {}, {}",
l,
l.len(),
rayon::current_num_threads()
);
let vec_local: Vec<i32> = vec![l.len() as i32];
}); // <-- line 54
}
Output produced by the cide is as follows:
line: '1__SEP__Lnumber 1__SEP__a__SEP__b__SEP__c' len: 41, 8
line: '3__SEP__Lnumber 9__SEP__g__SEP__h__SEP__i' len: 41, 8
line: '2__SEP__Lnumber 5__SEP__d__SEP__e__SEP__f' len: 41, 8
line: '4__SEP__Lnumber 13__SEP__j__SEP__k__SEP__l' len: 42, 8
File inp.log is as follows:
1
a
b
c
2
d
e
f
3
g
h
i
4
j
k
l
I was able to resolve the issue by using par_lines() instead as follows:
let tmp: Vec<_> = messages.par_lines().map(|l| proc_len(l)).collect();
...
...
...
fn proc_len(inp: &str) -> Vec<usize> {
let vec: Vec<usize> = vec![inp.len()];
return vec;
}
I'm using nom. I'd like to parse a string that's surrounded by parentheses, and allowing for additional nested parentheses within the string.
So (a + b) would parse as a + b, and ((a + b)) would parse as (a + b)
This works for the first case, but not the nested case:
pub fn parse_expr(input: &str) -> IResult<&str, &str> {
// TODO: this will fail with nested parentheses, but `rest` doesn't seem to
// be working.
delimited(tag("("), take_until(")"), tag(")"))(input)
}
I tried using rest but this doesn't respect the final ):
pub fn parse_expr(input: &str) -> IResult<&str, &str> {
delimited(tag("("), rest, tag(")"))(input)
}
Thanks!
I found a reference to this in the nom issue log: https://github.com/Geal/nom/issues/1253
I'm using this function, from parse_hyperlinks — basically a hand-written parser for this https://docs.rs/parse-hyperlinks/0.23.3/src/parse_hyperlinks/lib.rs.html#41 :
pub fn take_until_unbalanced(
opening_bracket: char,
closing_bracket: char,
) -> impl Fn(&str) -> IResult<&str, &str> {
move |i: &str| {
let mut index = 0;
let mut bracket_counter = 0;
while let Some(n) = &i[index..].find(&[opening_bracket, closing_bracket, '\\'][..]) {
index += n;
let mut it = i[index..].chars();
match it.next().unwrap_or_default() {
c if c == '\\' => {
// Skip the escape char `\`.
index += '\\'.len_utf8();
// Skip also the following char.
let c = it.next().unwrap_or_default();
index += c.len_utf8();
}
c if c == opening_bracket => {
bracket_counter += 1;
index += opening_bracket.len_utf8();
}
c if c == closing_bracket => {
// Closing bracket.
bracket_counter -= 1;
index += closing_bracket.len_utf8();
}
// Can not happen.
_ => unreachable!(),
};
// We found the unmatched closing bracket.
if bracket_counter == -1 {
// We do not consume it.
index -= closing_bracket.len_utf8();
return Ok((&i[index..], &i[0..index]));
};
}
if bracket_counter == 0 {
Ok(("", i))
} else {
Err(Err::Error(Error::from_error_kind(i, ErrorKind::TakeUntil)))
}
}
}
You can also consider this as, is it possible to URLify a string in place in rust?
For example,
Problem statement: Replace whitespace with %20
Assumption: String will have enough capacity left to accommodate new characters.
Input: Hello how are you
Output: Hello%20how%20are%20you
I know there are ways to do this if we don't have to do this "in place". I am solving a problem that explicitly states that you have to update in place.
If there isn't any safe way to do this, is there any particular reason behind that?
[Edit]
I was able to solve this using unsafe approach, but would appreciate a better approach than this. More idiomatic approach if there is.
fn space_20(sentence: &mut String) {
if !sentence.is_ascii() {
panic!("Invalid string");
}
let chars: Vec<usize> = sentence.char_indices().filter(|(_, ch)| ch.is_whitespace()).map(|(idx, _)| idx ).collect();
let char_count = chars.len();
if char_count == 0 {
return;
}
let sentence_len = sentence.len();
sentence.push_str(&"*".repeat(char_count*2)); // filling string with * so that bytes array becomes of required size.
unsafe {
let bytes = sentence.as_bytes_mut();
let mut final_idx = sentence_len + (char_count * 2) - 1;
let mut i = sentence_len - 1;
let mut char_ptr = char_count - 1;
loop {
if i != chars[char_ptr] {
bytes[final_idx] = bytes[i];
if final_idx == 0 {
// all elements are filled.
println!("all elements are filled.");
break;
}
final_idx -= 1;
} else {
bytes[final_idx] = '0' as u8;
bytes[final_idx - 1] = '2' as u8;
bytes[final_idx - 2] = '%' as u8;
// final_idx is of type usize cannot be less than 0.
if final_idx < 3 {
println!("all elements are filled at start.");
break;
}
final_idx -= 3;
// char_ptr is of type usize cannot be less than 0.
if char_ptr > 0 {
char_ptr -= 1;
}
}
if i == 0 {
// all elements are parsed.
println!("all elements are parsed.");
break;
}
i -= 1;
}
}
}
fn main() {
let mut sentence = String::with_capacity(1000);
sentence.push_str(" hello, how are you?");
// sentence.push_str("hello, how are you?");
// sentence.push_str(" hello, how are you? ");
// sentence.push_str(" ");
// sentence.push_str("abcd");
space_20(&mut sentence);
println!("{}", sentence);
}
An O(n) solution that neither uses unsafe nor allocates (provided that the string has enough capacity), using std::mem::take:
fn urlify_spaces(text: &mut String) {
const SPACE_REPLACEMENT: &[u8] = b"%20";
// operating on bytes for simplicity
let mut buffer = std::mem::take(text).into_bytes();
let old_len = buffer.len();
let space_count = buffer.iter().filter(|&&byte| byte == b' ').count();
let new_len = buffer.len() + (SPACE_REPLACEMENT.len() - 1) * space_count;
buffer.resize(new_len, b'\0');
let mut write_pos = new_len;
for read_pos in (0..old_len).rev() {
let byte = buffer[read_pos];
if byte == b' ' {
write_pos -= SPACE_REPLACEMENT.len();
buffer[write_pos..write_pos + SPACE_REPLACEMENT.len()]
.copy_from_slice(SPACE_REPLACEMENT);
} else {
write_pos -= 1;
buffer[write_pos] = byte;
}
}
*text = String::from_utf8(buffer).expect("invalid UTF-8 during URL-ification");
}
(playground)
Basically, it calculates the final length of the string, sets up a reading pointer and a writing pointer, and translates the string from right to left. Since "%20" has more characters than " ", the writing pointer never catches up with the reading pointer.
Is it possible to do this without unsafe?
Yes like this:
fn main() {
let mut my_string = String::from("Hello how are you");
let mut insert_positions = Vec::new();
let mut char_counter = 0;
for c in my_string.chars() {
if c == ' ' {
insert_positions.push(char_counter);
char_counter += 2; // Because we will insert two extra chars here later.
}
char_counter += 1;
}
for p in insert_positions.iter() {
my_string.remove(*p);
my_string.insert(*p, '0');
my_string.insert(*p, '2');
my_string.insert(*p, '%');
}
println!("{}", my_string);
}
Here is the Playground.
But should you do it?
As discussed for example here on Reddit this is almost always not the recommended way of doing this, because both remove and insert are O(n) operations as noted in the documentation.
Edit
A slightly better version:
fn main() {
let mut my_string = String::from("Hello how are you");
let mut insert_positions = Vec::new();
let mut char_counter = 0;
for c in my_string.chars() {
if c == ' ' {
insert_positions.push(char_counter);
char_counter += 2; // Because we will insert two extra chars here later.
}
char_counter += 1;
}
for p in insert_positions.iter() {
my_string.remove(*p);
my_string.insert_str(*p, "%20");
}
println!("{}", my_string);
}
and the corresponding Playground.
This code:
play
fn main() {
let text = "abcd";
for char in text.chars() {
if char == 'b' {
// skip 2 chars
}
print!("{}", char);
}
// prints `abcd`, but I want `ad`
}
prints abcd, but I want to skip 2 chars if b was found, so that it prints ad. How do I do that?
I tried to put the iterator into a variable outside the loop and manipulate that iterator within the loop, but the Borrow Checker doesn't allow that.
AFAIK you can't do that with a for loop. You will need to desugar it by hand:
let mut it = text.chars();
while let Some(char) = it.next() {
if char == 'b' {
it.nth(1); // nth(1) skips/consumes exactly 2 items
continue;
}
print!("{}", char);
}
Playground
If you want to keep an iterator style, you can use std::iter::successors (I've replaced the special char with '!' for being more readable:
fn my_iter<'a>(s: &'a str) -> impl Iterator<Item = char> + 'a {
let mut it = s.chars();
std::iter::successors(it.next(), move |c| {
if *c == '!' {
it.next().and_then(|_| it.next())
} else {
it.next()
}
})
.filter(|c| *c != '!')
}
fn main() {
assert!(my_iter("a!bc").eq("ac".chars()));
assert!(my_iter("!abcd").eq("bcd".chars()));
assert!(my_iter("abc!d").eq("abc".chars()));
assert!(my_iter("abcd!").eq("abcd".chars()));
}
I want to create a substring in Rust. It starts with an occurrence of a string and ends at the end of the string minus four characters or at a certain character.
My first approach was
string[string.find("pattern").unwrap()..string.len()-5]
That is wrong because Rust's strings are valid UTF-8 and thus byte and not char based.
My second approach is correct but too verbose:
let start_bytes = string.find("pattern").unwrap();
let mut char_byte_counter = 0;
let result = line.chars()
.skip_while(|c| {
char_byte_counter += c.len_utf8();
return start_bytes > char_byte_counter;
})
.take_while(|c| *c != '<')
.collect::<String>();
Are there simpler ways to create substrings? Is there any part of the standard library I did not find?
I don't remember a built-in library function in other languages that works exactly the way you want (give me the substring between two patterns, or between the first and the end if the second does not exist).
I think you would have to write some custom logic anyway.
The closest equivalent to a "substring" function is slicing. However (as you found out) it works with bytes, not with unicode characters, so you will have to be careful with indices. In "Löwe", the 'e' is at (byte) index 4, not 3 (playground). But you can still use it in your case, because you are not working with indices directly (using find instead to... find the index you need for you)
Here's how you could do it with slicing (bonus, you don't need to re-allocate other Strings):
// adding some unicode to check that everything works
// also ouside of ASCII
let line = "asdfapatterndf1老虎23<12";
let start_bytes = line.find("pattern").unwrap_or(0); //index where "pattern" starts
// or beginning of line if
// "pattern" not found
let end_bytes = line.find("<").unwrap_or(line.len()); //index where "<" is found
// or end of line
let result = &line[start_bytes..end_bytes]; //slicing line, returns patterndf1老虎23
Try using something like the following method:
//Return result in &str or empty &str if not found
fn between<'a>(source: &'a str, start: &'a str, end: &'a str) -> &'a str {
let start_position = source.find(start);
if start_position.is_some() {
let start_position = start_position.unwrap() + start.len();
let source = &source[start_position..];
let end_position = source.find(end).unwrap_or_default();
return &source[..end_position];
}
return "";
}
This method approximate to O(n) with char and grapheme in mind. It works, but I'm not sure if there are any bugs.
fn between(str: &String, start: String, end: String, limit_one:bool, ignore_case: bool) -> Vec<String> {
let mut result:Vec<String> = vec![];
let mut starts = start.graphemes(true);
let mut ends = end.graphemes(true);
let sc = start.graphemes(true).count();
let ec = end.graphemes(true).count();
let mut m = 0;
let mut started:bool = false;
let mut temp = String::from("");
let mut temp2 = String::from("");
for c in str.graphemes(true) {
if started == false {
let opt = starts.next();
match opt {
Some(d) => {
if (ignore_case && c.to_uppercase().cmp(&d.to_uppercase()) == std::cmp::Ordering::Equal) || c == d {
m += 1;
if m == sc {
started = true;
starts = start.graphemes(true);
}
} else {
m = 0;
starts = start.graphemes(true);
}
},
None => {
starts = start.graphemes(true);
let opt = starts.next();
match opt {
Some(e) => {
if (ignore_case && c.to_uppercase().cmp(&e.to_uppercase()) == std::cmp::Ordering::Equal) || c == e {
m += 1;
if m == sc {
started = true;
starts = start.graphemes(true);
}
}
},
None => {}
}
}
}
}
else if started == true {
let opt = ends.next();
match opt {
Some(e) => {
if (ignore_case && c.to_uppercase().cmp(&e.to_uppercase()) == std::cmp::Ordering::Equal) || c == e {
m += 1;
temp2.push_str(e);
}
else {
temp.push_str(&temp2.to_string());
temp2 = String::from("") ;
temp.push_str(c);
ends = end.graphemes(true);
}
},
None => {
ends = end.graphemes(true);
let opt = ends.next();
match opt {
Some(e) => {
if (ignore_case && c.to_uppercase().cmp(&e.to_uppercase()) == std::cmp::Ordering::Equal) || c == e {
m += 1;
temp2.push_str(e);
}
else {
temp.push_str(&temp2.to_string());
temp2 = String::from("") ;
temp.push_str(c);
ends = end.graphemes(true);
}
},
None => {
}
}
}
}
if temp2.graphemes(true).count() == end.graphemes(true).count() {
temp2 = String::from("") ;
result.push(temp);
if limit_one == true { return result; }
started = false;
temp = String::from("") ;
}
}
}
return result;
}