csv parsing: skip whitespace on failed parse (#2953)

polars/polars-io/src/csv_core/buffer.rs

@@ -1,5 +1,6 @@
 use crate::csv::CsvEncoding;
 use crate::csv_core::csv::RunningSize;
+use crate::csv_core::parser::{is_whitespace, skip_whitespace};
 use crate::csv_core::utils::escape_field;
 use arrow::array::Utf8Array;
 use arrow::bitmap::MutableBitmap;
@@ -85,10 +86,20 @@ where
             // its faster to work on options.
             // if we need to throw an error, we parse again to be able to throw the error
 
-            match (T::parse(bytes), ignore_errors) {
-                (Some(value), _) => self.append_value(value),
-                (None, true) => self.append_null(),
-                (None, _) => return Err(PolarsError::ComputeError("".into())),
+            match T::parse(bytes) {
+                Some(value) => self.append_value(value),
+                None => {
+                    // try again without whitespace
+                    if is_whitespace(bytes[0]) {
+                        let bytes = skip_whitespace(bytes);
+                        return self.parse_bytes(bytes, ignore_errors, needs_escaping);
+                    }
+                    if ignore_errors {
+                        self.append_null()
+                    } else {
+                        return Err(PolarsError::ComputeError("".into()));
+                    }
+                }
             };
         }
         Ok(())

polars/tests/it/io/csv.rs

@@ -983,3 +983,18 @@ fn test_parse_dates() -> Result<()> {
     assert_eq!(out.column("date")?.null_count(), 1);
     Ok(())
 }
+
+#[test]
+fn test_whitespace_skipping() -> Result<()> {
+    let csv = "a,b
+  12,   1435";
+    let file = Cursor::new(csv);
+    let out = CsvReader::new(file).finish()?;
+    let expected = df![
+        "a" => [12i64],
+        "b" => [1435i64],
+    ]?;
+    assert!(out.frame_equal(&expected));
+
+    Ok(())
+}