diff --git a/datastock/_class1.py b/datastock/_class1.py
index 29b9296..2c9644c 100644
--- a/datastock/_class1.py
+++ b/datastock/_class1.py
@@ -470,7 +470,6 @@ def extract(
             return_keys: returns the value of keys
 
         """
-
         return _class1_compute._extract_instance(
             self,
             keys=keys,
diff --git a/datastock/_class1_compute.py b/datastock/_class1_compute.py
index a204115..2418d85 100644
--- a/datastock/_class1_compute.py
+++ b/datastock/_class1_compute.py
@@ -735,7 +735,6 @@ def _extract_instance(
     # -----------------
     # select
     # -----------------
-
     ldata, lref = _extract_select(
         coll=coll,
         keys=keys,
@@ -755,7 +754,6 @@ def _extract_instance(
         else:
             coll2 = coll.__class__()
 
-
     # ------------------------
     # Populate
     # ------------------------
diff --git a/datastock/_plot_as_array.py b/datastock/_plot_as_array.py
index 4b6c33f..3b4d2d4 100644
--- a/datastock/_plot_as_array.py
+++ b/datastock/_plot_as_array.py
@@ -91,7 +91,7 @@ def plot_as_array(
 
     # check key, inplace flag and extract sub-collection
     lk = [kk for kk in [keyX, keyY, keyZ, keyU] if kk is not None]
-    coll2, key = coll.extract(
+    coll2, keys = coll.extract(
         [key] + lk,
         inc_monot=False,
         inc_vectors=False,
@@ -99,7 +99,10 @@ def plot_as_array(
         return_keys=True,
         inplace=inplace,
     )
-    key = [kk for kk in key if kk not in lk][0]
+    if key is None:
+        key = [kk for kk in key if kk not in lk]
+        lndim = [coll2.ddata[kk]['data'].ndim for kk in key]
+        key = key[np.argmax(lndim)]
     ndim = coll2.ddata[key]['data'].ndim
 
     # --------------
@@ -603,7 +606,6 @@ def _check(
         else:
             dvminmax2[k1]['min'] = dvminmax[kk]['min']
 
-
         if dvminmax is None or dvminmax.get(kk, {}).get('max') is None:
             dvminmax2[k1]['max'] = nanmax + margin
         else: