Method distinct

Return a new `DataFrame` with all duplicated rows removed. # Example ``` # use datafusion::prelude::*; # use datafusion::error::Result; # use datafusion_common::assert_batches_sorted_eq; # #[tokio::main] # async fn main() -> Result<()> { let ctx = SessionContext::new(); let df = ctx .read_csv("tests/data/example.csv", CsvReadOptions::new()) .await?; let df = df.distinct()?; let expected = vec![ "

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