chore(rust): Move diff to polars-ops

crates/polars-core/Cargo.toml

@@ -91,7 +91,6 @@ take_opt_iter = []
 group_by_list = []
 # rolling window functions
 rolling_window = []
-diff = []
 moment = []
 diagonal_concat = []
 horizontal_concat = []
@@ -147,7 +146,6 @@ docs-selection = [
   "dot_product",
   "row_hash",
   "rolling_window",
-  "diff",
   "moment",
   "dtype-categorical",
   "dtype-decimal",

crates/polars-core/src/series/ops/mod.rs

@@ -1,5 +1,3 @@
-#[cfg(feature = "diff")]
-pub mod diff;
 mod downcast;
 mod extend;
 #[cfg(feature = "moment")]

crates/polars-ops/Cargo.toml

@@ -82,8 +82,8 @@ to_dummies = []
 interpolate = []
 list_to_struct = ["polars-core/dtype-struct"]
 list_count = []
-diff = ["polars-core/diff"]
-pct_change = ["polars-core/diff"]
+diff = []
+pct_change = ["diff"]
 strings = ["polars-core/strings"]
 string_justify = ["polars-core/strings"]
 string_from_radix = ["polars-core/strings"]

crates/polars-ops/src/chunked_array/list/namespace.rs

@@ -17,6 +17,8 @@ use super::*;
 use crate::chunked_array::list::any_all::*;
 use crate::chunked_array::list::min_max::{list_max_function, list_min_function};
 use crate::chunked_array::list::sum_mean::sum_with_nulls;
+#[cfg(feature = "diff")]
+use crate::prelude::diff;
 use crate::prelude::list::sum_mean::{mean_list_numerical, sum_list_numerical};
 use crate::series::ArgAgg;
 
@@ -256,7 +258,7 @@ pub trait ListNameSpaceImpl: AsList {
     #[cfg(feature = "diff")]
     fn lst_diff(&self, n: i64, null_behavior: NullBehavior) -> PolarsResult<ListChunked> {
         let ca = self.as_list();
-        ca.try_apply_amortized(|s| s.as_ref().diff(n, null_behavior))
+        ca.try_apply_amortized(|s| diff(s.as_ref(), n, null_behavior))
     }
 
     fn lst_shift(&self, periods: &Series) -> PolarsResult<ListChunked> {

crates/polars-ops/src/series/ops/diff.rs

@@ -0,0 +1,22 @@
+use polars_core::prelude::*;
+use polars_core::series::ops::NullBehavior;
+
+pub fn diff(s: &Series, n: i64, null_behavior: NullBehavior) -> PolarsResult<Series> {
+    use DataType::*;
+    let s = match s.dtype() {
+        UInt8 => s.cast(&Int16)?,
+        UInt16 => s.cast(&Int32)?,
+        UInt32 | UInt64 => s.cast(&Int64)?,
+        _ => s.clone(),
+    };
+
+    match null_behavior {
+        NullBehavior::Ignore => Ok(&s - &s.shift(n)),
+        NullBehavior::Drop => {
+            polars_ensure!(n > 0, InvalidOperation: "only positive integer allowed if nulls are dropped in 'diff' operation");
+            let n = n as usize;
+            let len = s.len() - n;
+            Ok(&s.slice(n as i64, len) - &s.slice(0, len))
+        },
+    }
+}

crates/polars-ops/src/series/ops/mod.rs

@@ -7,6 +7,8 @@ mod clip;
 mod cum_agg;
 #[cfg(feature = "cutqcut")]
 mod cut;
+#[cfg(feature = "diff")]
+mod diff;
 #[cfg(feature = "ewma")]
 mod ewm;
 #[cfg(feature = "round_series")]
@@ -49,6 +51,8 @@ pub use clip::*;
 pub use cum_agg::*;
 #[cfg(feature = "cutqcut")]
 pub use cut::*;
+#[cfg(feature = "diff")]
+pub use diff::*;
 #[cfg(feature = "ewma")]
 pub use ewm::*;
 #[cfg(feature = "round_series")]

crates/polars-ops/src/series/ops/pct_change.rs

@@ -1,6 +1,8 @@
 use polars_core::prelude::*;
 use polars_core::series::ops::NullBehavior;
 
+use crate::prelude::diff;
+
 pub fn pct_change(s: &Series, n: &Series) -> PolarsResult<Series> {
     polars_ensure!(
         n.len() == 1,
@@ -16,9 +18,7 @@ pub fn pct_change(s: &Series, n: &Series) -> PolarsResult<Series> {
 
     let n_s = n.cast(&DataType::Int64)?;
     if let Some(n) = n_s.i64()?.get(0) {
-        fill_null_s
-            .diff(n, NullBehavior::Ignore)?
-            .divide(&fill_null_s.shift(n))
+        diff(&fill_null_s, n, NullBehavior::Ignore)?.divide(&fill_null_s.shift(n))
     } else {
         Ok(Series::full_null(s.name(), s.len(), s.dtype()))
     }

crates/polars-plan/Cargo.toml

@@ -107,7 +107,7 @@ rolling_window = [
   "polars-time/rolling_window",
 ]
 rank = ["polars-ops/rank"]
-diff = ["polars-core/diff", "polars-ops/diff"]
+diff = ["polars-ops/diff"]
 pct_change = ["polars-ops/pct_change"]
 moment = ["polars-core/moment", "polars-ops/moment"]
 abs = ["polars-core/abs"]

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

@@ -15,7 +15,7 @@ pub(super) fn approx_n_unique(s: &Series) -> PolarsResult<Series> {
 
 #[cfg(feature = "diff")]
 pub(super) fn diff(s: &Series, n: i64, null_behavior: NullBehavior) -> PolarsResult<Series> {
-    s.diff(n, null_behavior)
+    polars_ops::prelude::diff(s, n, null_behavior)
 }
 
 #[cfg(feature = "pct_change")]

crates/polars/Cargo.toml

@@ -143,7 +143,7 @@ cum_agg = ["polars-ops/cum_agg", "polars-lazy?/cum_agg"]
 rolling_window = ["polars-core/rolling_window", "polars-lazy?/rolling_window", "polars-time/rolling_window"]
 interpolate = ["polars-ops/interpolate", "polars-lazy?/interpolate"]
 rank = ["polars-lazy?/rank", "polars-ops/rank"]
-diff = ["polars-core/diff", "polars-lazy?/diff", "polars-ops/diff"]
+diff = ["polars-ops/diff", "polars-lazy?/diff"]
 pct_change = ["polars-ops/pct_change", "polars-lazy?/pct_change"]
 moment = ["polars-core/moment", "polars-lazy?/moment", "polars-ops/moment"]
 range = ["polars-lazy?/range"]