Merge pull request #2400 from midichef/merge_diff_empty

[join-] prevent diff error for empty merge cells

tests/golden/pr2400.tsv

@@ -0,0 +1,9 @@
+	a	b	c	Number	Exile
+  	d  	 e 	  f		
+1 	ggg	hhh	iiii		
+ 2	jjj	kkk	llllllll		
+Daniel				1	True
+Hananiah				2	True
+Mishael				3	True
+Azariah				4	True
+Nebuchadnezzar				5	

tests/pr2400.vdj

@@ -0,0 +1,19 @@
+#!vd -p
+{"sheet": "global", "col": null, "row": "disp_date_fmt", "longname": "set-option", "input": "%b %d, %Y", "keystrokes": "", "comment": null}
+{"sheet": "global", "row": "disp_float_fmt", "longname": "set-option", "input": "%.05f", "keystrokes": ""}
+{"sheet": "global", "row": "default_width", "longname": "set-option", "input": "50", "keystrokes": ""}
+{"longname": "open-file", "input": "sample_data/test.fixed", "keystrokes": "o"}
+{"longname": "open-file", "input": "sample_data/officials.jsonla", "keystrokes": "o"}
+{"sheet": "test", "col": "", "row": "", "longname": "sheets-stack", "input": "", "keystrokes": "Shift+S", "comment": "open Sheets Stack: join or jump between the active sheets on the current stack"}
+{"sheet": "sheets", "col": "", "row": "\u30adofficials", "longname": "open-row", "input": "", "keystrokes": "Enter", "comment": "open sheet referenced in current row"}
+{"sheet": "officials", "col": "", "row": "", "longname": "sheets-stack", "input": "", "keystrokes": "Shift+S", "comment": "open Sheets Stack: join or jump between the active sheets on the current stack"}
+{"sheet": "sheets", "col": "", "row": "\u30adsheets", "longname": "open-row", "input": "", "keystrokes": "Enter", "comment": "open sheet referenced in current row"}
+{"sheet": "sheets", "col": "", "row": "\u30adofficials", "longname": "open-row", "input": "", "keystrokes": "Enter", "comment": "open sheet referenced in current row"}
+{"sheet": "officials", "col": "Name", "row": "", "longname": "key-col", "input": "", "keystrokes": "!", "comment": "toggle current column as a key column"}
+{"sheet": "officials", "col": "", "row": "", "longname": "sheets-stack", "input": "", "keystrokes": "Shift+S", "comment": "open Sheets Stack: join or jump between the active sheets on the current stack"}
+{"sheet": "sheets", "col": "", "row": "\u30adtest", "longname": "open-row", "input": "", "keystrokes": "Enter", "comment": "open sheet referenced in current row"}
+{"sheet": "test", "col": 0, "row": "", "longname": "key-col", "input": "", "keystrokes": "!", "comment": "toggle current column as a key column"}
+{"sheet": "test", "col": "", "row": "", "longname": "sheets-stack", "input": "", "keystrokes": "Shift+S", "comment": "open Sheets Stack: join or jump between the active sheets on the current stack"}
+{"sheet": "sheets", "col": "", "row": "\u30adtest", "longname": "stoggle-row", "input": "", "keystrokes": "t", "comment": "toggle selection of current row"}
+{"sheet": "sheets", "col": "", "row": "\u30adofficials", "longname": "stoggle-row", "input": "", "keystrokes": "t", "comment": "toggle selection of current row"}
+{"sheet": "sheets", "col": "", "row": "", "longname": "join-selected", "input": "merge", "keystrokes": "&", "comment": "merge selected sheets with visible columns from all, keeping rows according to jointype"}

visidata/features/join.py

@@ -167,7 +167,11 @@ def putValue(self, row, value):
 
     def isDiff(self, row, value):
         col = list(self.cols.values())[0]
-        return col and value != col.getValue(row[col.sheet])
+        if not col:
+            return False
+        if row[col.sheet] is None:
+            return True
+        return value != col.getValue(row[col.sheet])
 
 
 #### slicing and dicing
@@ -196,6 +200,7 @@ def loader(self):
         self.setKeys(self.columns)
 
         allcols = collections.defaultdict(dict) # colname: { sheet: origcol, ... }
+        # MergeColumn relies on allcols having sheets in this specific order
         for sheetnum, vs in enumerate(sheets):
             for c in vs.visibleCols:
                 if c not in self.sheetKeyCols[vs]: