MetaArray: make it possible to append multiple axis values

Example use case: taking an image stack where each frame has a time value AND a position. Previously we could only append new time values.

pyqtgraph/metaarray/MetaArray.py

@@ -748,7 +748,6 @@ class MetaArray(object):
             else:
                 fd.seek(0)
                 meta = MetaArray._readMeta(fd)
-
                 if not kwargs.get("readAllData", True):
                     self._data = np.empty(meta['shape'], dtype=meta['type'])
                 if 'version' in meta:
@@ -1031,6 +1030,7 @@ class MetaArray(object):
         """Write this object to a file. The object can be restored by calling MetaArray(file=fileName)
         opts:
             appendAxis: the name (or index) of the appendable axis. Allows the array to grow.
+            appendKeys: a list of keys (other than "values") for metadata to append to on the appendable axis.
             compression: None, 'gzip' (good compression), 'lzf' (fast compression), etc.
             chunks: bool or tuple specifying chunk shape
         """
@@ -1096,7 +1096,6 @@ class MetaArray(object):
                 'chunks': None,
                 'compression': None
             }
-        
             
         ## set maximum shape to allow expansion along appendAxis
         append = False
@@ -1125,14 +1124,19 @@ class MetaArray(object):
             data[tuple(sl)] = self.view(np.ndarray)
             
             ## add axis values if they are present.
+            axKeys = ["values"]
+            axKeys.extend(opts.get("appendKeys", []))
             axInfo = f['info'][str(ax)]
-            if 'values' in axInfo:
-                v = axInfo['values']
-                v2 = self._info[ax]['values']
-                shape = list(v.shape)
-                shape[0] += v2.shape[0]
-                v.resize(shape)
-                v[-v2.shape[0]:] = v2
+            for key in axKeys:
+                if key in axInfo:
+                    v = axInfo[key]
+                    v2 = self._info[ax][key]
+                    shape = list(v.shape)
+                    shape[0] += v2.shape[0]
+                    v.resize(shape)
+                    v[-v2.shape[0]:] = v2
+                else:
+                    raise TypeError('Cannot append to axis info key "%s"; this key is not present in the target file.' % key)
             f.close()
         else:
             f = h5py.File(fileName, 'w')