Update _join.py (#1108)

* Update _join.py

Added error message for multidimensional axes. This checks all data objects. I thought that would be of use given that one may have to define 1D versions of variable axes for all objects, and could make a mistake in one but not all of the 'datas' to be joined. Open to discussion.

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* Update _join.py

Updated changelog, used a more specific wt_exception

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CHANGELOG.md

@@ -6,6 +6,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/).
 ## [Unreleased]
 
 ## Changed
+- data.join now has MultidimensionalAxisError exception message
 - `Axis`: space character ("\s") in expressions are culled.
 - fixed `interact2D` bug: channel/axes can now be specified with non-zero index arguments
 

WrightTools/data/_join.py

@@ -88,6 +88,10 @@ def join(
     for d in datas[1:]:
         if d.axis_expressions != axis_expressions:
             raise wt_exceptions.ValueError("Joined data must have same axis_expressions")
+        for a in d.axes:
+            if a.variables[0][:].squeeze().ndim > 1:
+                raise wt_exceptions.MultidimensionalAxisError(a.natural_name, "join")
+
         variable_names &= set(d.variable_names)
         channel_names &= set(d.channel_names)
     variable_names = list(variable_names)
@@ -103,6 +107,8 @@ def join(
     for a in datas[0].axes:
         if len(a.variables) > 1:
             raise wt_exceptions.ValueError("Applied transform must have single variable axes")
+        if a.variables[0][:].squeeze().ndim > 1:
+            raise wt_exceptions.MultidimensionalAxisError(a.natural_name, "join")
         for v in a.variables:
             axis_variable_names.append(v.natural_name)
             axis_variable_units.append(v.units)