29 lines
853 B
Plaintext
29 lines
853 B
Plaintext
use std::error::Error;
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use std::num::ParseIntError;
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use csv::{Reader, Writer};
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fn main() -> Result<(), Box<dyn Error>> {
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let mut reader = Reader::from_path("data.csv")?;
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let mut writer = Writer::from_path("output.csv")?;
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// headers() returns an immutable reference, so clone() before appending
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let mut headers = reader.headers()?.clone();
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headers.push_field("SUM");
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writer.write_record(headers.iter())?;
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for row in reader.records() {
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let mut row = row?;
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// `sum` needs the type annotation so that `parse::<i64>` knows what error type to return
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let sum: Result<_, ParseIntError> = row.iter().try_fold(0, |accum, s| {
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Ok(accum + s.parse::<i64>()?)
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});
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row.push_field(&sum?.to_string());
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writer.write_record(row.iter())?;
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}
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writer.flush()?;
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Ok(())
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}
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