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The Results of the Expressive C++17 Coding Challenge in Rust
use std::env;
use std::io;
use std::io::prelude::*;
use std::fs::File;
#[derive(Debug)]
enum Error {
Io(io::Error),
Program(&'static str),
}
impl From<io::Error> for Error {
fn from(e: io::Error) -> Error {
Error::Io(e)
}
}
impl From<&'static str> for Error {
fn from(e: &'static str) -> Error {
Error::Program(e)
}
}
fn main() {
let mut args = env::args();
// skip the program name
args.next().unwrap();
let filename = args.next().unwrap();
let column_name = args.next().unwrap();
let replacement = args.next().unwrap();
let output_filename = args.next().unwrap();
let csv_data = load_csv(&filename).unwrap();
let modified_data = replace_column(csv_data, &column_name, &replacement).unwrap();
write_csv(&modified_data, &output_filename).unwrap();
}
fn load_csv(filename: &str) -> Result<String, Error> {
let mut f = File::open(filename)?;
let mut buffer = String::new();
f.read_to_string(&mut buffer)?;
if buffer.is_empty() {
return Err("input file missing")?
}
Ok(buffer)
}
fn replace_column(data: String, column: &str, replacement: &str) -> Result<String, Error> {
let mut lines = data.lines();
let columns = lines.next().unwrap();
let columns: Vec<&str> = columns.split(',').collect();
let column_number = columns.iter().position(|&e| e == column);
let column_number = match column_number {
Some(column) => column,
None => Err("column name doesn’t exist in the input file")?
};
let mut result = String::with_capacity(data.capacity());
result.push_str(&columns.join(","));
result.push('\n');
for line in lines {
let mut records: Vec<&str> = line.split(',').collect();
records[column_number] = replacement;
result.push_str(&records.join(","));
result.push('\n');
}
Ok(result)
}
fn write_csv(data: &str, filename: &str) -> Result<(), Error> {
let mut buffer = File::create(filename)?;
buffer.write_all(data.as_bytes())?;
Ok(())
}
@matharumanpreet00

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matharumanpreet00 commented Oct 26, 2017

Beautiful !!!

@locka99

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locka99 commented Oct 26, 2017

Looks a lot more readable than the winning C++17 entry

@pacman82

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pacman82 commented Oct 26, 2017

Nice, yet I have to nitpick that the winning C++ entry does not load the entire input file into memory. Wrapping the file into a std::io::BufReader instead of saving it to a string would do the trick, since BufRead also exposes a lines() iterator.

@msehnout

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msehnout commented Nov 1, 2017

I like some aspects of the C++ version more, so I decided to combine them into my own version. Also there is a problem, that the winning entry does not respect the rule In both cases, there shouldn’t be any output file generated.. I decided to obey this rule, although it makes the code less nice, because of the split of the get_file_handlers function.
https://gist.github.com/msehnout/6b6a964b4ce87df104f67aefdcb0585c

@boxdot

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boxdot commented Nov 4, 2017

@msehnout: I totally agree that for big csv it could a problem to read everything into memory. Another issue could be: not necessary mallocs inside the iteratation over the lines. Actually, there is no need for creating any temporary vectors or strings at all: https://gist.github.com/boxdot/8abd5eccec95dd74d0a35d33463ae53b

I was too lazy to define From impls, which definitely a better approach than using String as universal error wrapper.

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