diff --git a/src/pscpy/psc.py b/src/pscpy/psc.py
index 54c2bb6..bf1e606 100644
--- a/src/pscpy/psc.py
+++ b/src/pscpy/psc.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from collections.abc import Iterable
+from collections.abc import Generator, Hashable, Iterable
 from typing import Any
 
 import numpy as np
@@ -50,52 +50,16 @@ def __repr__(self) -> str:
         return f"Psc(gdims={self.gdims}, length={self.length}, corner={self.corner})"
 
 
-def get_field_to_component(species_names: Iterable[str]) -> dict[str, dict[str, int]]:
-    field_to_component: dict[str, dict[str, int]] = {}
-    field_to_component["jeh"] = {
-        "jx_ec": 0,
-        "jy_ec": 1,
-        "jz_ec": 2,
-        "ex_ec": 3,
-        "ey_ec": 4,
-        "ez_ec": 5,
-        "hx_fc": 6,
-        "hy_fc": 7,
-        "hz_fc": 8,
-    }
-    field_to_component["dive"] = {"dive": 0}
-    field_to_component["rho"] = {"rho": 0}
-    field_to_component["d_rho"] = {"d_rho": 0}
-    field_to_component["dt_divj"] = {"dt_divj": 0}
-
-    # keeping 'all_1st' for backwards compatibility
-    field_to_component["all_1st"] = {}
-    field_to_component["all_1st_cc"] = {}
-    moments = [
-        "rho",
-        "jx",
-        "jy",
-        "jz",
-        "px",
-        "py",
-        "pz",
-        "txx",
-        "tyy",
-        "tzz",
-        "txy",
-        "tyz",
-        "tzx",
-    ]
-    for species_idx, species_name in enumerate(species_names):
-        for moment_idx, moment in enumerate(moments):
-            field_to_component["all_1st"][f"{moment}_{species_name}"] = (
-                moment_idx + 13 * species_idx
-            )
-            field_to_component["all_1st_cc"][f"{moment}_{species_name}"] = (
-                moment_idx + 13 * species_idx
-            )
-
-    return field_to_component
+def iter_components(field: Hashable, species_names: Iterable[str]) -> Generator[str]:
+    if field == "jeh":
+        yield from ["jx_ec", "jy_ec", "jz_ec", "ex_ec", "ey_ec", "ez_ec", "hx_fc", "hy_fc", "hz_fc"]  # fmt: off
+    elif field in ["dive", "rho", "d_rho", "dt_divj"]:
+        yield str(field)
+    elif field in ["all_1st", "all_1st_cc"]:
+        moments = ["rho", "jx", "jy", "jz", "px", "py", "pz", "txx", "tyy", "tzz", "txy", "tyz", "tzx"]  # fmt: off
+        for species_name in species_names:
+            for moment in moments:
+                yield f"{moment}_{species_name}"
 
 
 def decode_psc(
@@ -118,15 +82,13 @@ def decode_psc(
             }
         )
     ds = ds.squeeze("step")
-    field_to_component = get_field_to_component(species_names)
 
-    data_vars = {}
     for var_name in ds:
-        if var_name in field_to_component:
-            for field, component_idx in field_to_component[var_name].items():  # type: ignore[index]
-                data_vars[field] = ds[var_name][component_idx, :, :, :]
+        for component_idx, component in enumerate(
+            iter_components(var_name, species_names)
+        ):
+            ds = ds.assign({component: ds[var_name][component_idx, :, :, :]})
         ds = ds.drop_vars([var_name])
-    ds = ds.assign(data_vars)
 
     run_info = RunInfo(ds, length=length, corner=corner)
     coords = {