Added parquet functionality. Version bump

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "dr"
 description = "Command-line data file processing in Rust"
-version = "0.2.1"
+version = "0.3.0"
 edition = "2021"
 include = [
     "**/*.rs",

README.md

@@ -53,6 +53,7 @@ Commands:
   sql    Runs a sql statement on the file
   print  Pretty prints the table
   rpq    Read parquet file
+  wpq    Write to a parquet file
   help   Print this message or the help of the given subcommand(s)
 
 Options:
@@ -82,13 +83,41 @@ shape: (4, 14)
 
 Note that when `dr` loads csv data also tries to guess the data type of each field.
 
+### Parquet
+
+`dr` is also useful to translate your csv files to parquet with a single command:
+
+```bash
+$ cat wine.csv | dr wpq wine.pq
+```
+
+Or explore parquet files
+
+```bash
+$ dr rpq wine.pq | head -n 5 | dr print
+shape: (4, 14)
+┌──────┬─────────┬────────────┬──────┬─────┬───────────┬──────┬──────┬─────────┐
+│ Wine ┆ Alcohol ┆ Malic.acid ┆ Ash  ┆ ... ┆ Color.int ┆ Hue  ┆ OD   ┆ Proline │
+│ ---  ┆ ---     ┆ ---        ┆ ---  ┆     ┆ ---       ┆ ---  ┆ ---  ┆ ---     │
+│ i64  ┆ f64     ┆ f64        ┆ f64  ┆     ┆ f64       ┆ f64  ┆ f64  ┆ i64     │
+╞══════╪═════════╪════════════╪══════╪═════╪═══════════╪══════╪══════╪═════════╡
+│ 1    ┆ 14.23   ┆ 1.71       ┆ 2.43 ┆ ... ┆ 5.64      ┆ 1.04 ┆ 3.92 ┆ 1065    │
+├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┼╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┼╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┤
+│ 1    ┆ 13.2    ┆ 1.78       ┆ 2.14 ┆ ... ┆ 4.38      ┆ 1.05 ┆ 3.4  ┆ 1050    │
+├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┼╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┼╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┤
+│ 1    ┆ 13.16   ┆ 2.36       ┆ 2.67 ┆ ... ┆ 5.68      ┆ 1.03 ┆ 3.17 ┆ 1185    │
+├╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┼╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌┼╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌┤
+│ 1    ┆ 14.37   ┆ 1.95       ┆ 2.5  ┆ ... ┆ 7.8       ┆ 0.86 ┆ 3.45 ┆ 1480    │
+└──────┴─────────┴────────────┴──────┴─────┴───────────┴──────┴──────┴─────────┘
+```
+
 
 ## Performance
 
 `dr` is implemented in Rust with the goal of achieving the highest possible performance. Take for instance a simple read, groupby, and aggregate operation with ~30MB of data:
 
 ```bash
-$ time cat data/walmart_train.csv | ./target/release/dr sql "select Dept, avg("Weekly_Sales") from this group by Dept" | ./target/release/dr print
+$ time cat data/walmart_train.csv | dr sql "select Dept, avg("Weekly_Sales") from this group by Dept" | dr print
 shape: (81, 2)
 ┌──────┬──────────────┐
 │ Dept ┆ Weekly_Sales │

src/io.rs

@@ -39,3 +39,30 @@ pub fn read_parquet(path: String) -> DataFrame {
     };
     df
 }
+
+/// Write a Polars DataFrame to Parquet
+pub fn write_parquet(
+    mut df: DataFrame,
+    path: String,
+    compression: String,
+    statistics: bool,
+    chunksize: Option<usize>,
+) {
+    // Selected compression not implemented yet
+    let mut _file = match fs::File::create(path) {
+        Ok(mut file) => {
+            let mut w = ParquetWriter::new(&mut file);
+            if statistics {
+                w = w.with_statistics(statistics);
+            }
+            if chunksize.unwrap_or(0) > 0 {
+                w = w.with_row_group_size(chunksize);
+            }
+            let _r = match w.finish(&mut df) {
+                Ok(_r) => (),
+                Err(e) => eprintln!("{e}"),
+            };
+        }
+        Err(e) => eprintln!("{e}"),
+    };
+}

src/main.rs

@@ -16,6 +16,11 @@ fn main() {
                 .about("Read parquet file")
                 .arg(arg!([path] "Path to the parquet file")),
         )
+        .subcommand(
+            Command::new("wpq")
+                .about("Write to a paquet file")
+                .arg(arg!([path] "Path to the new parquet file")),
+        )
         .get_matches();
 
     if let Some(matches) = matches.subcommand_matches("sql") {
@@ -40,6 +45,13 @@ fn main() {
         } else {
             eprintln!("File not found")
         }
+    } else if let Some(matches) = matches.subcommand_matches("wpq") {
+        if let Some(path) = matches.get_one::<String>("path") {
+            let df = io::load_csv_from_stdin();
+            io::write_parquet(df, path.to_string(), "lz4raw".to_string(), true, Some(0));
+        } else {
+            eprintln!("Could now write to parquet");
+        }
     } else {
         println!("No command provided. Please execute dr --help")
     }