polars_lazy/scan/
csv.rs

1#[cfg(feature = "csv")]
2use polars_buffer::Buffer;
3use polars_core::prelude::*;
4use polars_io::cloud::CloudOptions;
5use polars_io::csv::read::{
6    CommentPrefix, CsvEncoding, CsvParseOptions, CsvReadOptions, NullValues,
7    read_until_start_and_infer_schema,
8};
9use polars_io::path_utils::expand_paths;
10use polars_io::utils::compression::CompressedReader;
11use polars_io::{HiveOptions, RowIndex};
12use polars_utils::mmap::MMapSemaphore;
13use polars_utils::pl_path::PlRefPath;
14use polars_utils::slice_enum::Slice;
15
16use crate::prelude::*;
17
18#[derive(Clone)]
19#[cfg(feature = "csv")]
20pub struct LazyCsvReader {
21    sources: ScanSources,
22    glob: bool,
23    cache: bool,
24    read_options: CsvReadOptions,
25    cloud_options: Option<CloudOptions>,
26    include_file_paths: Option<PlSmallStr>,
27}
28
29#[cfg(feature = "csv")]
30impl LazyCsvReader {
31    /// Re-export to shorten code.
32    pub fn map_parse_options<F: Fn(CsvParseOptions) -> CsvParseOptions>(
33        mut self,
34        map_func: F,
35    ) -> Self {
36        self.read_options = self.read_options.map_parse_options(map_func);
37        self
38    }
39
40    pub fn new_paths(paths: Buffer<PlRefPath>) -> Self {
41        Self::new_with_sources(ScanSources::Paths(paths))
42    }
43
44    pub fn new_with_sources(sources: ScanSources) -> Self {
45        LazyCsvReader {
46            sources,
47            glob: true,
48            cache: true,
49            read_options: Default::default(),
50            cloud_options: Default::default(),
51            include_file_paths: None,
52        }
53    }
54
55    pub fn new(path: PlRefPath) -> Self {
56        Self::new_with_sources(ScanSources::Paths(Buffer::from_iter([path])))
57    }
58
59    /// Skip this number of rows after the header location.
60    #[must_use]
61    pub fn with_skip_rows_after_header(mut self, offset: usize) -> Self {
62        self.read_options.skip_rows_after_header = offset;
63        self
64    }
65
66    /// Add a row index column.
67    #[must_use]
68    pub fn with_row_index(mut self, row_index: Option<RowIndex>) -> Self {
69        self.read_options.row_index = row_index;
70        self
71    }
72
73    /// Try to stop parsing when `n` rows are parsed. During multithreaded parsing the upper bound `n` cannot
74    /// be guaranteed.
75    #[must_use]
76    pub fn with_n_rows(mut self, num_rows: Option<usize>) -> Self {
77        self.read_options.n_rows = num_rows;
78        self
79    }
80
81    /// Sets the number of threads used for CSV parsing.
82    #[must_use]
83    pub fn with_n_threads(mut self, n_threads: Option<usize>) -> Self {
84        self.read_options.n_threads = n_threads;
85        self
86    }
87
88    /// Set the number of rows to use when inferring the csv schema.
89    /// The default is 100 rows.
90    /// Setting to [None] will do a full table scan, which is very slow.
91    #[must_use]
92    pub fn with_infer_schema_length(mut self, num_rows: Option<usize>) -> Self {
93        self.read_options.infer_schema_length = num_rows;
94        self
95    }
96
97    /// Continue with next batch when a ParserError is encountered.
98    #[must_use]
99    pub fn with_ignore_errors(mut self, ignore: bool) -> Self {
100        self.read_options.ignore_errors = ignore;
101        self
102    }
103
104    /// Set the CSV file's schema
105    #[must_use]
106    pub fn with_schema(mut self, schema: Option<SchemaRef>) -> Self {
107        self.read_options.schema = schema;
108        self
109    }
110
111    /// Skip the first `n` rows during parsing. The header will be parsed at row `n`.
112    /// Note that by row we mean valid CSV, encoding and comments are respected.
113    #[must_use]
114    pub fn with_skip_rows(mut self, skip_rows: usize) -> Self {
115        self.read_options.skip_rows = skip_rows;
116        self
117    }
118
119    /// Skip the first `n` lines during parsing. The header will be parsed at line `n`.
120    /// We don't respect CSV escaping when skipping lines.
121    #[must_use]
122    pub fn with_skip_lines(mut self, skip_lines: usize) -> Self {
123        self.read_options.skip_lines = skip_lines;
124        self
125    }
126
127    /// Overwrite the schema with the dtypes in this given Schema. The given schema may be a subset
128    /// of the total schema.
129    #[must_use]
130    pub fn with_dtype_overwrite(mut self, schema: Option<SchemaRef>) -> Self {
131        self.read_options.schema_overwrite = schema;
132        self
133    }
134
135    /// Set whether the CSV file has headers
136    #[must_use]
137    pub fn with_has_header(mut self, has_header: bool) -> Self {
138        self.read_options.has_header = has_header;
139        self
140    }
141
142    /// Sets the chunk size used by the parser. This influences performance.
143    /// This can be used as a way to reduce memory usage during the parsing at the cost of performance.
144    pub fn with_chunk_size(mut self, chunk_size: usize) -> Self {
145        self.read_options.chunk_size = chunk_size;
146        self
147    }
148
149    /// Set the CSV file's column separator as a byte character
150    #[must_use]
151    pub fn with_separator(self, separator: u8) -> Self {
152        self.map_parse_options(|opts| opts.with_separator(separator))
153    }
154
155    /// Set the comment prefix for this instance. Lines starting with this prefix will be ignored.
156    #[must_use]
157    pub fn with_comment_prefix(self, comment_prefix: Option<PlSmallStr>) -> Self {
158        self.map_parse_options(|opts| {
159            opts.with_comment_prefix(comment_prefix.clone().map(|s| {
160                if s.len() == 1 && s.chars().next().unwrap().is_ascii() {
161                    CommentPrefix::Single(s.as_bytes()[0])
162                } else {
163                    CommentPrefix::Multi(s)
164                }
165            }))
166        })
167    }
168
169    /// Set the `char` used as quote char. The default is `b'"'`. If set to [`None`] quoting is disabled.
170    #[must_use]
171    pub fn with_quote_char(self, quote_char: Option<u8>) -> Self {
172        self.map_parse_options(|opts| opts.with_quote_char(quote_char))
173    }
174
175    /// Set the `char` used as end of line. The default is `b'\n'`.
176    #[must_use]
177    pub fn with_eol_char(self, eol_char: u8) -> Self {
178        self.map_parse_options(|opts| opts.with_eol_char(eol_char))
179    }
180
181    /// Set values that will be interpreted as missing/ null.
182    #[must_use]
183    pub fn with_null_values(self, null_values: Option<NullValues>) -> Self {
184        self.map_parse_options(|opts| opts.with_null_values(null_values.clone()))
185    }
186
187    /// Treat missing fields as null.
188    pub fn with_missing_is_null(self, missing_is_null: bool) -> Self {
189        self.map_parse_options(|opts| opts.with_missing_is_null(missing_is_null))
190    }
191
192    /// Cache the DataFrame after reading.
193    #[must_use]
194    pub fn with_cache(mut self, cache: bool) -> Self {
195        self.cache = cache;
196        self
197    }
198
199    /// Reduce memory usage at the expense of performance
200    #[must_use]
201    pub fn with_low_memory(mut self, low_memory: bool) -> Self {
202        self.read_options.low_memory = low_memory;
203        self
204    }
205
206    /// Set  [`CsvEncoding`]
207    #[must_use]
208    pub fn with_encoding(self, encoding: CsvEncoding) -> Self {
209        self.map_parse_options(|opts| opts.with_encoding(encoding))
210    }
211
212    /// Automatically try to parse dates/datetimes and time.
213    /// If parsing fails, columns remain of dtype [`DataType::String`].
214    #[cfg(feature = "temporal")]
215    pub fn with_try_parse_dates(self, try_parse_dates: bool) -> Self {
216        self.map_parse_options(|opts| opts.with_try_parse_dates(try_parse_dates))
217    }
218
219    /// Raise an error if CSV is empty (otherwise return an empty frame)
220    #[must_use]
221    pub fn with_raise_if_empty(mut self, raise_if_empty: bool) -> Self {
222        self.read_options.raise_if_empty = raise_if_empty;
223        self
224    }
225
226    /// Truncate lines that are longer than the schema.
227    #[must_use]
228    pub fn with_truncate_ragged_lines(self, truncate_ragged_lines: bool) -> Self {
229        self.map_parse_options(|opts| opts.with_truncate_ragged_lines(truncate_ragged_lines))
230    }
231
232    #[must_use]
233    pub fn with_decimal_comma(self, decimal_comma: bool) -> Self {
234        self.map_parse_options(|opts| opts.with_decimal_comma(decimal_comma))
235    }
236
237    #[must_use]
238    /// Expand path given via globbing rules.
239    pub fn with_glob(mut self, toggle: bool) -> Self {
240        self.glob = toggle;
241        self
242    }
243
244    pub fn with_cloud_options(mut self, cloud_options: Option<CloudOptions>) -> Self {
245        self.cloud_options = cloud_options;
246        self
247    }
248
249    /// Modify a schema before we run the lazy scanning.
250    ///
251    /// Important! Run this function latest in the builder!
252    pub fn with_schema_modify<F>(mut self, f: F) -> PolarsResult<Self>
253    where
254        F: Fn(Schema) -> PolarsResult<Schema>,
255    {
256        let n_threads = self.read_options.n_threads;
257
258        let infer_schema = |bytes: Buffer<u8>| {
259            let mut reader = CompressedReader::try_new(bytes)?;
260
261            let (inferred_schema, _) =
262                read_until_start_and_infer_schema(&self.read_options, None, None, &mut reader)?;
263
264            PolarsResult::Ok(inferred_schema)
265        };
266
267        let schema = match self.sources.clone() {
268            ScanSources::Paths(paths) => {
269                // TODO: Path expansion should happen when converting to the IR
270                // https://github.com/pola-rs/polars/issues/17634
271
272                use polars_io::pl_async::get_runtime;
273
274                let paths = get_runtime().block_on(expand_paths(
275                    &paths[..],
276                    self.glob(),
277                    &[], // hidden_file_prefix
278                    &mut self.cloud_options,
279                ))?;
280
281                let Some(path) = paths.first() else {
282                    polars_bail!(ComputeError: "no paths specified for this reader");
283                };
284
285                let file = polars_utils::open_file(path.as_std_path())?;
286                let mmap = MMapSemaphore::new_from_file(&file)?;
287                infer_schema(Buffer::from_owner(mmap))?
288            },
289            ScanSources::Files(files) => {
290                let Some(file) = files.first() else {
291                    polars_bail!(ComputeError: "no buffers specified for this reader");
292                };
293
294                let mmap = MMapSemaphore::new_from_file(file)?;
295                infer_schema(Buffer::from_owner(mmap))?
296            },
297            ScanSources::Buffers(buffers) => {
298                let Some(buffer) = buffers.first() else {
299                    polars_bail!(ComputeError: "no buffers specified for this reader");
300                };
301
302                infer_schema(buffer.clone())?
303            },
304        };
305
306        self.read_options.n_threads = n_threads;
307        let mut schema = f(schema)?;
308
309        // the dtypes set may be for the new names, so update again
310        if let Some(overwrite_schema) = &self.read_options.schema_overwrite {
311            for (name, dtype) in overwrite_schema.iter() {
312                schema.with_column(name.clone(), dtype.clone());
313            }
314        }
315
316        Ok(self.with_schema(Some(Arc::new(schema))))
317    }
318
319    pub fn with_include_file_paths(mut self, include_file_paths: Option<PlSmallStr>) -> Self {
320        self.include_file_paths = include_file_paths;
321        self
322    }
323}
324
325impl LazyFileListReader for LazyCsvReader {
326    /// Get the final [LazyFrame].
327    fn finish(self) -> PolarsResult<LazyFrame> {
328        let rechunk = self.rechunk();
329        let row_index = self.row_index().cloned();
330        let pre_slice = self.n_rows().map(|len| Slice::Positive { offset: 0, len });
331
332        let lf: LazyFrame = DslBuilder::scan_csv(
333            self.sources,
334            self.read_options,
335            UnifiedScanArgs {
336                schema: None,
337                cloud_options: self.cloud_options,
338                hive_options: HiveOptions::new_disabled(),
339                rechunk,
340                cache: self.cache,
341                glob: self.glob,
342                hidden_file_prefix: None,
343                projection: None,
344                column_mapping: None,
345                default_values: None,
346                row_index,
347                pre_slice,
348                cast_columns_policy: CastColumnsPolicy::ERROR_ON_MISMATCH,
349                missing_columns_policy: MissingColumnsPolicy::Raise,
350                extra_columns_policy: ExtraColumnsPolicy::Raise,
351                include_file_paths: self.include_file_paths,
352                deletion_files: None,
353                table_statistics: None,
354                row_count: None,
355            },
356        )?
357        .build()
358        .into();
359        Ok(lf)
360    }
361
362    fn finish_no_glob(self) -> PolarsResult<LazyFrame> {
363        unreachable!();
364    }
365
366    fn glob(&self) -> bool {
367        self.glob
368    }
369
370    fn sources(&self) -> &ScanSources {
371        &self.sources
372    }
373
374    fn with_sources(mut self, sources: ScanSources) -> Self {
375        self.sources = sources;
376        self
377    }
378
379    fn with_n_rows(mut self, n_rows: impl Into<Option<usize>>) -> Self {
380        self.read_options.n_rows = n_rows.into();
381        self
382    }
383
384    fn with_row_index(mut self, row_index: impl Into<Option<RowIndex>>) -> Self {
385        self.read_options.row_index = row_index.into();
386        self
387    }
388
389    fn rechunk(&self) -> bool {
390        self.read_options.rechunk
391    }
392
393    /// Rechunk the memory to contiguous chunks when parsing is done.
394    fn with_rechunk(mut self, rechunk: bool) -> Self {
395        self.read_options.rechunk = rechunk;
396        self
397    }
398
399    /// Try to stop parsing when `n` rows are parsed. During multithreaded parsing the upper bound `n` cannot
400    /// be guaranteed.
401    fn n_rows(&self) -> Option<usize> {
402        self.read_options.n_rows
403    }
404
405    /// Return the row index settings.
406    fn row_index(&self) -> Option<&RowIndex> {
407        self.read_options.row_index.as_ref()
408    }
409
410    fn concat_impl(&self, lfs: Vec<LazyFrame>) -> PolarsResult<LazyFrame> {
411        // set to false, as the csv parser has full thread utilization
412        let args = UnionArgs {
413            rechunk: self.rechunk(),
414            parallel: false,
415            to_supertypes: false,
416            from_partitioned_ds: true,
417            ..Default::default()
418        };
419        concat_impl(&lfs, args)
420    }
421
422    /// [CloudOptions] used to list files.
423    fn cloud_options(&self) -> Option<&CloudOptions> {
424        self.cloud_options.as_ref()
425    }
426}
polars_lazy/scan/csv.rs

polars_lazy/scan/
csv.rs
