Method count

datafusion/core/src/dataframe/mod.rs:1423–1440

Return the total number of rows in this `DataFrame`. Note that this method will actually run a plan to calculate the count, which may be slow for large or complicated DataFrames. # Example ``` # use datafusion::prelude::*; # use datafusion::error::Result; # #[tokio::main] # async fn main() -> Result<()> { let ctx = SessionContext::new(); let df = ctx .read_csv("tests/data/example.csv", CsvReadOp

(self)

    /// # }
    /// ```
    pub async fn count(self) -> Result<usize> {
        let rows = self
            .aggregate(
                vec![],
                vec![count(Expr::Literal(COUNT_STAR_EXPANSION, None))],
            )?
            .collect()
            .await?;
        let len = *rows
            .first()
            .and_then(|r| r.columns().first())
            .and_then(|c| c.as_any().downcast_ref::<Int64Array>())
            .and_then(|a| a.values().first())
            .ok_or_else(|| {
                internal_datafusion_err!("Unexpected output when collecting for count()")
            })? as usize;
        Ok(len)
    }

    /// Execute this `DataFrame` and buffer all resulting `RecordBatch`es  into memory.
    ///