--- a/table-union.py	Fri Mar 09 11:14:02 2018 -0500
+++ b/table-union.py	Tue Oct 30 16:18:02 2018 -0400
@@ -4,7 +4,7 @@
 
 
 
-def main(files):
+def main(unionize=True, *files):
 	header = []
 	items = []
 	possible_identity_headers = None
@@ -15,6 +15,8 @@
 			for field in reader.fieldnames:
 				if field not in set(header):
 					header.append(field)
+				
+					
 				#try to find identity columns in the files, to use to join
 				if possible_identity_headers is None:
 					possible_identity_headers = set(reader.fieldnames)
@@ -30,7 +32,7 @@
 	# 	possible_identity_headers = set((possible_identity_headers.pop(), ))
 
 	#if we found an identity column, then try to join rows
-	if possible_identity_headers:
+	if possible_identity_headers and unionize:
 		key_column = possible_identity_headers.pop()
 		keys = set([r[key_column] for r in items])
 		merged_rows = []
@@ -47,4 +49,4 @@
 
 
 if __name__ == '__main__':
-	main(sys.argv[1:])
\ No newline at end of file
+	main(*sys.argv[1:])
\ No newline at end of file

--- a/table-union.xml	Fri Mar 09 11:14:02 2018 -0500
+++ b/table-union.xml	Tue Oct 30 16:18:02 2018 -0400
@@ -4,14 +4,32 @@
         <!-- <requirement type="package" version="3.4">python</requirement> -->
     </requirements>
     <command detect_errors="exit_code"><![CDATA[
-        python $__tool_directory__/table-union.py 
+    	#if $input_type.source_select == 'two'
+    	#set tables=($table_1, $table_2)
+    	#else
+    	#set tables=$input_type.tables
+    	#end if
+        python $__tool_directory__/table-union.py "$union"
         #for $table in $tables
             $table
         #end for
         > $combined_table
     ]]></command>
     <inputs>
-        <param name="tables" type="data_collection" format="tsv" collection_type="list" />
+    	<param name="union" type="boolean" label="Attempt to unionize on an autodetected key column" checked="false" falsevalue="" />
+    	<conditional name="input_type">
+    		<param name="source_select" type="select" label="Mode">
+    			<option value="two">Combine two tables</option>
+    			<option value="collection">Combine a collection of tables</option>
+    		</param>
+    		<when value="collection">
+       			<param name="tables" type="data_collection" format="tabular,tsv" collection_type="list" />
+       		</when>
+       		<when value="two">
+       			<param name="table_1" type="data" format="tabular,tsv" />
+       			<param name="table_2" type="data" format="tabular,tsv" />
+       		</when>
+        </conditional>
     </inputs>
     <outputs>
         <data name="combined_table" format="tsv" label="Combined table" />
@@ -19,6 +37,8 @@
 
     <tests>
         <test>
+        	<param name="source_select" value="collection" />
+        	<param name="union" value="true" />
             <param name="tables">
                 <collection type="list">
                     <element name="1" value="dingbat.tsv" />
@@ -27,6 +47,13 @@
             </param>
             <output name="combined_table" value="combined.tsv" />
         </test>
+        <test>
+        	<param name="source_select" value="two" />
+        	<param name="union" value="false" />
+        	<param name="table_1" value="dingbat.tsv" />
+        	<param name="table_2" value="loki.tsv" />
+        	<output name="combined_table" value="no_union.tsv" />
+        </test>
     </tests>
     <help><![CDATA[
         Concatenate a collection of TSV files wile preserving and unionizing headers.

--- a/test-data/combined.tsv	Fri Mar 09 11:14:02 2018 -0500
+++ b/test-data/combined.tsv	Tue Oct 30 16:18:02 2018 -0400
@@ -1,4 +1,4 @@
-name	flavor	size	color
-Dingbat	strawberry		red
-Dunston	strawberry	massive	blue
-Loki	chocolate	massive	
+name	flavor	color	size
+Dingbat	strawberry	red	
+Dunston	strawberry	blue	massive
+Loki	chocolate		massive

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test-data/no_union.tsv	Tue Oct 30 16:18:02 2018 -0400
@@ -0,0 +1,5 @@
+name	flavor	color	size
+Dingbat	strawberry	red	
+Dunston	strawberry	blue	
+Loki	chocolate		massive
+Dunston	strawberry		massive