Alter field values

src/earthkit/data/core/fieldlist.py

@@ -729,7 +729,7 @@ def _attributes(self, names, remapping=None, joiner=None, default=None):
 
         # return {name: metadata(name) for name in names}
 
-    def to_field(self, array_backend=None, **kwargs):
+    def to_field(self, flatten=False, dtype=None, array_backend=None, values=None, **kwargs):
         r"""Convert to a new :class:`Field`.
 
         Parameters
@@ -748,7 +748,17 @@ def to_field(self, array_backend=None, **kwargs):
         """
         from earthkit.data.sources.array_list import ArrayField
 
-        return ArrayField(self.to_array(array_backend=array_backend, **kwargs), self._metadata.override())
+        if values is None:
+            values = self.to_array(
+                flatten=flatten,
+                dtype=dtype,
+                array_backend=array_backend,
+            )
+
+        return ArrayField(
+            values,
+            self._metadata.override(**kwargs),
+        )
 
     @staticmethod
     def _flatten(v):

src/earthkit/data/indexing/fieldlist.py

@@ -124,5 +124,33 @@ def _metadata(self):
         return self.__metadata
 
 
+class NewFieldWrapper:
+    def __init__(self, field, values=None, **kwargs):
+        self._field = field
+        self.__values = values
+
+        if kwargs:
+            from earthkit.data.core.metadata import WrappedMetadata
+
+            self.__metadata = WrappedMetadata(field._metadata, extra=kwargs, owner=field)
+        else:
+            self.__metadata = field._metadata
+
+    def _values(self, dtype=None):
+        if self.__values is None:
+            return self._field._values(dtype=dtype)
+        else:
+            if dtype is None:
+                return self.__values
+            return self.__values.astype(dtype)
+
+    @property
+    def _metadata(self):
+        return self.__metadata
+
+    def _has_new_values(self):
+        return self.__values is not None
+
+
 # For backwards compatibility
 FieldArray = SimpleFieldList

src/earthkit/data/readers/grib/codes.py

@@ -15,7 +15,7 @@
 import numpy as np
 
 from earthkit.data.core.fieldlist import Field
-from earthkit.data.indexing.fieldlist import NewFieldMetadataWrapper
+from earthkit.data.indexing.fieldlist import NewFieldWrapper
 from earthkit.data.readers.grib.metadata import GribFieldMetadata
 from earthkit.data.utils.message import CodesHandle
 from earthkit.data.utils.message import CodesMessagePositionIndex
@@ -326,12 +326,12 @@ def message(self):
         return self.handle.get_buffer()
 
     def copy(self, **kwargs):
-        return NewMetadataGribField(self, **kwargs)
+        return NewGribField(self, **kwargs)
 
 
-class NewMetadataGribField(NewFieldMetadataWrapper, GribField):
+class NewGribField(NewFieldWrapper, GribField):
     def __init__(self, field, **kwargs):
-        NewFieldMetadataWrapper.__init__(self, field, **kwargs)
+        NewFieldWrapper.__init__(self, field, **kwargs)
         self._handle = field._handle
         GribField.__init__(
             self,

src/earthkit/data/readers/grib/memory.py

@@ -11,7 +11,7 @@
 
 import eccodes
 
-from earthkit.data.indexing.fieldlist import NewFieldMetadataWrapper
+from earthkit.data.indexing.fieldlist import NewFieldWrapper
 from earthkit.data.indexing.fieldlist import SimpleFieldList
 from earthkit.data.readers import Reader
 from earthkit.data.readers.grib.codes import GribCodesHandle
@@ -156,12 +156,12 @@ def from_buffer(buf):
         )
 
     def copy(self, **kwargs):
-        return NewMetadataGribFieldInMemory(self, **kwargs)
+        return NewGribFieldInMemory(self, **kwargs)
 
 
-class NewMetadataGribFieldInMemory(NewFieldMetadataWrapper, GribFieldInMemory):
+class NewGribFieldInMemory(NewFieldWrapper, GribFieldInMemory):
     def __init__(self, field, **kwargs):
-        NewFieldMetadataWrapper.__init__(self, field, **kwargs)
+        NewFieldWrapper.__init__(self, field, **kwargs)
         self._handle = field._handle
         GribFieldInMemory.__init__(
             self,

src/earthkit/data/readers/netcdf/field.py

@@ -17,7 +17,7 @@
 from earthkit.data.core.geography import Geography
 from earthkit.data.core.metadata import MetadataAccessor
 from earthkit.data.core.metadata import RawMetadata
-from earthkit.data.indexing.fieldlist import NewFieldMetadataWrapper
+from earthkit.data.indexing.fieldlist import NewFieldWrapper
 from earthkit.data.utils.bbox import BoundingBox
 from earthkit.data.utils.dates import to_datetime
 
@@ -296,12 +296,12 @@ def tidy(x):
         return tidy(self._ds[self._ds[self.variable].grid_mapping].attrs)
 
     def copy(self, **kwargs):
-        return NewMetadataXarrayField(self, **kwargs)
+        return NewXarrayField(self, **kwargs)
 
 
-class NewMetadataXarrayField(NewFieldMetadataWrapper, XArrayField):
+class NewXarrayField(NewFieldWrapper, XArrayField):
     def __init__(self, field, **kwargs):
-        NewFieldMetadataWrapper.__init__(self, field, **kwargs)
+        NewFieldWrapper.__init__(self, field, **kwargs)
         XArrayField.__init__(self, field.ds, field.variable, field.slices, field.non_dim_coords)
 
 

src/earthkit/data/sources/array_list.py

@@ -11,7 +11,7 @@
 import math
 
 from earthkit.data.core.fieldlist import Field
-from earthkit.data.indexing.fieldlist import NewFieldMetadataWrapper
+from earthkit.data.indexing.fieldlist import NewFieldWrapper
 from earthkit.data.utils.array import array_namespace
 
 LOG = logging.getLogger(__name__)
@@ -96,12 +96,12 @@ def __setstate__(self, state: dict):
         self.__metadata = state.pop("_metadata")
 
     def copy(self, **kwargs):
-        return NewMetadataArrayField(self, **kwargs)
+        return NewArrayField(self, **kwargs)
 
 
-class NewMetadataArrayField(NewFieldMetadataWrapper, ArrayField):
+class NewArrayField(NewFieldWrapper, ArrayField):
     def __init__(self, field, **kwargs):
-        NewFieldMetadataWrapper.__init__(self, field, **kwargs)
+        NewFieldWrapper.__init__(self, field, **kwargs)
         ArrayField.__init__(self, field._array, None)
 
 

src/earthkit/data/sources/forcings.py

@@ -20,7 +20,7 @@
 from earthkit.data.core.metadata import RawMetadata
 from earthkit.data.decorators import cached_method
 from earthkit.data.decorators import normalize
-from earthkit.data.indexing.fieldlist import NewFieldMetadataWrapper
+from earthkit.data.indexing.fieldlist import NewFieldWrapper
 from earthkit.data.utils.dates import to_datetime
 
 LOG = logging.getLogger(__name__)
@@ -256,15 +256,15 @@ def _values(self, dtype=None):
         return values
 
     def copy(self, **kwargs):
-        return NewMetadataForcingField(self, **kwargs)
+        return NewForcingField(self, **kwargs)
 
     def __repr__(self):
         return "ForcingField(%s,%s,%s)" % (self.param, self.date, self.number)
 
 
-class NewMetadataForcingField(NewFieldMetadataWrapper, ForcingField):
+class NewForcingField(NewFieldWrapper, ForcingField):
     def __init__(self, field, **kwargs):
-        NewFieldMetadataWrapper.__init__(self, field, **kwargs)
+        NewFieldWrapper.__init__(self, field, **kwargs)
         ForcingField.__init__(self, field.maker, field.date, field.param, field.proc, number=field.number)
 
 

src/earthkit/data/writers/grib.py

@@ -48,6 +48,13 @@ def write(self, f, field, values=None, check_nans=True, bits_per_value=None):
         if "generatingProcessIdentifier" not in md:
             md["generatingProcessIdentifier"] = None
 
+        if values is None:
+            try:
+                if field._has_new_values():
+                    values = field.values
+            except AttributeError:
+                pass
+
         output.write(values, check_nans=check_nans, missing_value=field.handle.MISSING_VALUE, **md)