Remove use of dask.array.ma in PCA in favour of array API compliant f…

…unctions

sgkit/stats/preprocessing.py

@@ -62,8 +62,8 @@ def fit(
             Alternate allele counts with missing values encoded as either nan
             or negative numbers.
         """
-        X = da.ma.masked_array(X, mask=da.isnan(X) | (X < 0))
-        self.mean_ = da.ma.filled(da.mean(X, axis=0), fill_value=np.nan)
+        X = _replace_missing_with_nan(X)
+        self.mean_ = da.nanmean(X, axis=0)
         p = self.mean_ / self.ploidy
         self.scale_ = da.sqrt(p * (1 - p))
         self.n_features_in_ = X.shape[1]
@@ -90,10 +90,10 @@ def transform(
             Alternate allele counts with missing values encoded as either nan
             or negative numbers.
         """
-        X = da.ma.masked_array(X, mask=da.isnan(X) | (X < 0))
+        X = _replace_missing_with_nan(X)
         X -= self.mean_
         X /= self.scale_
-        return da.ma.filled(X, fill_value=np.nan)
+        return X
 
     def inverse_transform(self, X: ArrayLike, copy: Optional[bool] = None) -> ArrayLike:
         """Invert transform
@@ -109,6 +109,14 @@ def inverse_transform(self, X: ArrayLike, copy: Optional[bool] = None) -> ArrayL
         return X
 
 
+def _replace_missing_with_nan(X):
+    if np.issubdtype(X.dtype, np.floating):
+        nanarray = da.asarray(np.nan, dtype=X.dtype)
+    else:
+        nanarray = da.asarray(np.nan)
+    return da.where(X < 0, nanarray, X)
+
+
 def filter_partial_calls(
     ds: Dataset,
     *,