polars_lazy/scan/
csv.rs

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

polars_lazy/scan/
csv.rs
