depr(python,rust!): Deprecate str.explode in favor of str.split("").explode()

crates/polars-core/src/chunked_array/ops/explode_and_offsets.rs

@@ -1,8 +1,5 @@
-use arrow::bitmap::MutableBitmap;
-use arrow::compute::cast::utf8view_to_utf8;
 use arrow::compute::take::take_unchecked;
 use arrow::offset::OffsetsBuffer;
-use polars_utils::vec::PushUnchecked;
 
 use super::*;
 
@@ -233,135 +230,3 @@ impl ChunkExplode for ArrayChunked {
         ))
     }
 }
-
-impl ChunkExplode for StringChunked {
-    fn offsets(&self) -> PolarsResult<OffsetsBuffer<i64>> {
-        let mut offsets = Vec::with_capacity(self.len() + 1);
-        let mut length_so_far = 0;
-        offsets.push(length_so_far);
-
-        for arr in self.downcast_iter() {
-            for len in arr.len_iter() {
-                // SAFETY:
-                // pre-allocated
-                unsafe { offsets.push_unchecked(length_so_far) };
-                length_so_far += len as i64;
-            }
-        }
-
-        // SAFETY:
-        // Monotonically increasing.
-        unsafe { Ok(OffsetsBuffer::new_unchecked(offsets.into())) }
-    }
-
-    fn explode_and_offsets(&self) -> PolarsResult<(Series, OffsetsBuffer<i64>)> {
-        // A list array's memory layout is actually already 'exploded', so we can just take the values array
-        // of the list. And we also return a slice of the offsets. This slice can be used to find the old
-        // list layout or indexes to expand the DataFrame in the same manner as the 'explode' operation
-        let ca = self.rechunk();
-        let array = ca.downcast_iter().next().unwrap();
-        // TODO! maybe optimize for new utf8view?
-        let array = utf8view_to_utf8(array);
-
-        let values = array.values();
-        let old_offsets = array.offsets().clone();
-
-        let (new_offsets, validity) = if let Some(validity) = array.validity() {
-            // capacity estimate
-            let capacity = self.get_values_size() + validity.unset_bits();
-
-            let old_offsets = old_offsets.as_slice();
-            let mut old_offset = old_offsets[0];
-            let mut new_offsets = Vec::with_capacity(capacity + 1);
-            new_offsets.push(old_offset);
-
-            let mut bitmap = MutableBitmap::with_capacity(capacity);
-            let values = values.as_slice();
-            for (&offset, valid) in old_offsets[1..].iter().zip(validity) {
-                // SAFETY:
-                // new_offsets already has a single value, so -1 is always in bounds
-                let latest_offset = unsafe { *new_offsets.get_unchecked(new_offsets.len() - 1) };
-
-                if valid {
-                    debug_assert!(old_offset as usize <= values.len());
-                    debug_assert!(offset as usize <= values.len());
-                    let val = unsafe { values.get_unchecked(old_offset as usize..offset as usize) };
-
-                    // take the string value and find the char offsets
-                    // create a new offset value for each char boundary
-                    // SAFETY:
-                    // we know we have string data.
-                    let str_val = unsafe { std::str::from_utf8_unchecked(val) };
-
-                    let char_offsets = str_val
-                        .char_indices()
-                        .skip(1)
-                        .map(|t| t.0 as i64 + latest_offset);
-
-                    // extend the chars
-                    // also keep track of the amount of offsets added
-                    // as we must update the validity bitmap
-                    let len_before = new_offsets.len();
-                    new_offsets.extend(char_offsets);
-                    new_offsets.push(latest_offset + str_val.len() as i64);
-                    bitmap.extend_constant(new_offsets.len() - len_before, true);
-                } else {
-                    // no data, just add old offset and set null bit
-                    new_offsets.push(latest_offset);
-                    bitmap.push(false)
-                }
-                old_offset = offset;
-            }
-
-            (new_offsets.into(), bitmap.into())
-        } else {
-            // fast(er) explode
-
-            // we cannot naively explode, because there might be empty strings.
-
-            // capacity estimate
-            let capacity = self.get_values_size();
-            let old_offsets = old_offsets.as_slice();
-            let mut old_offset = old_offsets[0];
-            let mut new_offsets = Vec::with_capacity(capacity + 1);
-            new_offsets.push(old_offset);
-
-            let values = values.as_slice();
-            for &offset in &old_offsets[1..] {
-                // SAFETY:
-                // new_offsets already has a single value, so -1 is always in bounds
-                let latest_offset = unsafe { *new_offsets.get_unchecked(new_offsets.len() - 1) };
-                debug_assert!(old_offset as usize <= values.len());
-                debug_assert!(offset as usize <= values.len());
-                let val = unsafe { values.get_unchecked(old_offset as usize..offset as usize) };
-
-                // take the string value and find the char offsets
-                // create a new offset value for each char boundary
-                // SAFETY:
-                // we know we have string data.
-                let str_val = unsafe { std::str::from_utf8_unchecked(val) };
-
-                let char_offsets = str_val
-                    .char_indices()
-                    .skip(1)
-                    .map(|t| t.0 as i64 + latest_offset);
-
-                // extend the chars
-                new_offsets.extend(char_offsets);
-                new_offsets.push(latest_offset + str_val.len() as i64);
-                old_offset = offset;
-            }
-
-            (new_offsets.into(), None)
-        };
-
-        let array = unsafe {
-            Utf8Array::<i64>::from_data_unchecked_default(new_offsets, values.clone(), validity)
-        };
-
-        let new_arr = Box::new(array) as ArrayRef;
-
-        let s = Series::try_from((self.name(), new_arr)).unwrap();
-        Ok((s, old_offsets))
-    }
-}

crates/polars-plan/src/dsl/function_expr/strings.rs

@@ -39,7 +39,6 @@ pub enum StringFunction {
     },
     CountMatches(bool),
     EndsWith,
-    Explode,
     Extract(usize),
     ExtractAll,
     #[cfg(feature = "extract_groups")]
@@ -137,7 +136,6 @@ impl StringFunction {
             Contains { .. } => mapper.with_dtype(DataType::Boolean),
             CountMatches(_) => mapper.with_dtype(DataType::UInt32),
             EndsWith | StartsWith => mapper.with_dtype(DataType::Boolean),
-            Explode => mapper.with_same_dtype(),
             Extract(_) => mapper.with_same_dtype(),
             ExtractAll => mapper.with_dtype(DataType::List(Box::new(DataType::String))),
             #[cfg(feature = "extract_groups")]
@@ -208,7 +206,6 @@ impl Display for StringFunction {
             ConcatHorizontal { .. } => "concat_horizontal",
             #[cfg(feature = "concat_str")]
             ConcatVertical { .. } => "concat_vertical",
-            Explode => "explode",
             ExtractAll => "extract_all",
             #[cfg(feature = "extract_groups")]
             ExtractGroups { .. } => "extract_groups",
@@ -365,7 +362,6 @@ impl From<StringFunction> for SpecialEq<Arc<dyn SeriesUdf>> {
             Base64Encode => map!(strings::base64_encode),
             #[cfg(feature = "binary_encoding")]
             Base64Decode(strict) => map!(strings::base64_decode, strict),
-            Explode => map!(strings::explode),
             #[cfg(feature = "dtype-decimal")]
             ToDecimal(infer_len) => map!(strings::to_decimal, infer_len),
             #[cfg(feature = "extract_jsonpath")]
@@ -972,11 +968,6 @@ pub(super) fn base64_decode(s: &Series, strict: bool) -> PolarsResult<Series> {
     s.str()?.base64_decode(strict).map(|ca| ca.into_series())
 }
 
-pub(super) fn explode(s: &Series) -> PolarsResult<Series> {
-    let ca = s.str()?;
-    ca.explode()
-}
-
 #[cfg(feature = "dtype-decimal")]
 pub(super) fn to_decimal(s: &Series, infer_len: usize) -> PolarsResult<Series> {
     let ca = s.str()?;

crates/polars-plan/src/dsl/string.rs

@@ -547,11 +547,6 @@ impl StringNameSpace {
         )
     }
 
-    pub fn explode(self) -> Expr {
-        self.0
-            .apply_private(FunctionExpr::StringExpr(StringFunction::Explode))
-    }
-
     #[cfg(feature = "extract_jsonpath")]
     pub fn json_decode(self, dtype: Option<DataType>, infer_schema_len: Option<usize>) -> Expr {
         self.0

py-polars/polars/expr/expr.py

@@ -4952,7 +4952,6 @@ def explode(self) -> Self:
         See Also
         --------
         Expr.list.explode : Explode a list column.
-        Expr.str.explode : Explode a string column.
 
         Examples
         --------

py-polars/polars/expr/string.py

@@ -6,6 +6,7 @@
 import polars._reexport as pl
 from polars import functions as F
 from polars._utils.deprecation import (
+    deprecate_function,
     deprecate_renamed_function,
     deprecate_renamed_parameter,
     issue_deprecation_warning,
@@ -2352,10 +2353,23 @@ def tail(self, n: int | IntoExprColumn) -> Expr:
         n = parse_as_expression(n)
         return wrap_expr(self._pyexpr.str_tail(n))
 
+    @deprecate_function(
+        'Use `.str.split("").explode()` instead.'
+        " Note that empty strings will result in null instead of being preserved."
+        " To get the exact same behavior, split first and then use when/then/otherwise"
+        " to handle the empty list before exploding.",
+        version="0.20.31",
+    )
     def explode(self) -> Expr:
         """
         Returns a column with a separate row for every string character.
 
+        .. deprecated:: 0.20.31
+            Use `.str.split("").explode()` instead.
+            Note that empty strings will result in null instead of being preserved.
+            To get the exact same behavior, split first and then use when/then/otherwise
+            to handle the empty list before exploding.
+
         Returns
         -------
         Expr
@@ -2364,7 +2378,7 @@ def explode(self) -> Expr:
         Examples
         --------
         >>> df = pl.DataFrame({"a": ["foo", "bar"]})
-        >>> df.select(pl.col("a").str.explode())
+        >>> df.select(pl.col("a").str.explode())  # doctest: +SKIP
         shape: (6, 1)
         ┌─────┐
         │ a   │
@@ -2379,7 +2393,8 @@ def explode(self) -> Expr:
         │ r   │
         └─────┘
         """
-        return wrap_expr(self._pyexpr.str_explode())
+        split = self.split("")
+        return F.when(split.ne_missing([])).then(split).otherwise([""]).explode()
 
     def to_integer(
         self, *, base: int | IntoExprColumn = 10, strict: bool = True

py-polars/polars/series/series.py

@@ -4080,7 +4080,6 @@ def explode(self) -> Series:
         See Also
         --------
         Series.list.explode : Explode a list column.
-        Series.str.explode : Explode a string column.
 
         Examples
         --------

py-polars/polars/series/string.py

@@ -3,6 +3,7 @@
 from typing import TYPE_CHECKING
 
 from polars._utils.deprecation import (
+    deprecate_function,
     deprecate_renamed_function,
     deprecate_renamed_parameter,
 )
@@ -1776,10 +1777,23 @@ def tail(self, n: int | IntoExprColumn) -> Series:
         ]
         """
 
+    @deprecate_function(
+        'Use `.str.split("").explode()` instead.'
+        " Note that empty strings will result in null instead of being preserved."
+        " To get the exact same behavior, split first and then use when/then/otherwise"
+        " to handle the empty list before exploding.",
+        version="0.20.31",
+    )
     def explode(self) -> Series:
         """
         Returns a column with a separate row for every string character.
 
+        .. deprecated:: 0.20.31
+            Use `.str.split("").explode()` instead.
+            Note that empty strings will result in null instead of being preserved.
+            To get the exact same behavior, split first and then use when/then/otherwise
+            to handle the empty list before exploding.
+
         Returns
         -------
         Series
@@ -1788,7 +1802,7 @@ def explode(self) -> Series:
         Examples
         --------
         >>> s = pl.Series("a", ["foo", "bar"])
-        >>> s.str.explode()
+        >>> s.str.explode()  # doctest: +SKIP
         shape: (6,)
         Series: 'a' [str]
         [

py-polars/src/expr/string.rs

@@ -110,10 +110,6 @@ impl PyExpr {
         self.inner.clone().str().tail(n.inner).into()
     }
 
-    fn str_explode(&self) -> Self {
-        self.inner.clone().str().explode().into()
-    }
-
     fn str_to_uppercase(&self) -> Self {
         self.inner.clone().str().to_uppercase().into()
     }

py-polars/src/lazyframe/visitor/expr_nodes.rs

@@ -116,7 +116,6 @@ pub enum PyStringFunction {
     Contains,
     CountMatches,
     EndsWith,
-    Explode,
     Extract,
     ExtractAll,
     ExtractGroups,
@@ -675,9 +674,6 @@ pub(crate) fn into_py(py: Python<'_>, expr: &AExpr) -> PyResult<PyObject> {
                     StringFunction::EndsWith => {
                         (PyStringFunction::EndsWith.into_py(py),).to_object(py)
                     },
-                    StringFunction::Explode => {
-                        (PyStringFunction::Explode.into_py(py),).to_object(py)
-                    },
                     StringFunction::Extract(_) => {
                         (PyStringFunction::Extract.into_py(py),).to_object(py)
                     },