diff --git a/src/msspec/looper.py b/src/msspec/looper.py
index 192acb3..ce846d4 100644
--- a/src/msspec/looper.py
+++ b/src/msspec/looper.py
@@ -134,7 +134,7 @@ class SweepRange:
                     row[key] = value
                 else:
                     idx = int(i/(self.ntot/self.cn[isweep])) % len(sweep)
-        
+
                     # If this sweep has links, add also all values from its
                     # children
                     children = self.links.get(sweep, [])
@@ -168,7 +168,7 @@ class SweepRange:
 
 class Looper:
     def __init__(self):
-        pass
+        self.data = None
 
     @property
     def pipeline(self):
@@ -184,7 +184,7 @@ class Looper:
     def _wrapper(self, x):
         logger.debug("Pipeline called with {}".format(x))
         return self.pipeline(**x)
-        
+
     def run(self, *sweeps, ncpu=1, passindex=False):
         logger.info("Loop starts...")
         # prepare the list of inputs
@@ -213,7 +213,7 @@ class Looper:
             logger.info(("Parallel processing over {:d} cpu (chunksize={:d})..."
                          "").format(ncpu, chunksize))
             t0 = time.time()
-    
+
             pool = mp.Pool(processes=ncpu)
             data = pool.map(self._wrapper, items, chunksize=chunksize)
             pool.close()
@@ -235,6 +235,7 @@ class Looper:
 
         df = pd.DataFrame(dfdata, columns=columns)
 
+        self.data = df
         return df
 
 
@@ -284,4 +285,4 @@ if __name__ == "__main__":
     data = looper.run(emitter, emitter_plane, uij, theta, levels, ncpu=1,
                       passindex=True)
 
-    print(data)
+    print(data[data.emitter_plane.eq(0)].theta.unique())