CSVediting.md

@@ -88,7 +88,9 @@ preceding comma.
 
 ## Matching and Deleting a Row
 
-Suppose that we have a regular expression R to select CSV rows for deletion.  
+Suppose that we have a regular expression R to select CSV rows for deletion,
+where R has no Unicode properties or other features.
+
 The Parabix regular expression engine can be used to perform the matching and
 `FilterByMask` can be used for the deletion.
 
@@ -103,6 +105,41 @@ Using the ICGrepKernel to perform the matching may be implemented as follows.
     P->CreateKernelCall<ICGrepKernel>(std::move(options));
 ```
 
+The resulting `MatchResults` stream will have 1 bits on any matching CSV row.
+To select the row, the next task is to move the matches to the line end position,
+assuming that the line ends are given by `mLineBreakStream`.
+
+```
+StreamSet * const MovedMatches = P->CreateStreamSet();
+P->CreateKernelCall<MatchedLinesKernel>(MatchResults, mLineBreakStream, MovedMatches);
+```
+
+We can next get a stream that is indexed by line number (1 bit per CSV row).
+```
+StreamSet * MatchesByLine = P->CreateStreamSet(1, 1);
+FilterByMask(P, mLineBreakStream, MovedMatches, MatchesByLine);
+```
+
+LineStarts can then be identified as the positions immediately after a line break
+or at the beginning of the file.   These are computed by the `LineStartsKernel`.
 
+```
+StreamSet * LineStarts = E->CreateStreamSet(1, 1);
+P->CreateKernelCall<LineStartsKernel>(mLineBreakStream, LineStarts);
+```
+
+The starts of the matched lines are now computed by a  ```SpreadByMask```.
+```
+StreamSet * MatchedLineStarts = E->CreateStreamSet(1, 1);
+SpreadByMask(E, LineStarts, MatchesByLine, MatchedLineStarts);
+```
+
+Now a mask for an entire matched row can be computed, using the LineSpansKernel.
+```
+StreamSet * MatchedLineSpans = E->CreateStreamSet(1, 1);
+P->CreateKernelCall<LineSpansKernel>(MatchedLineStarts, MatchedLineEnds, MatchedLineSpans);
+```
 
+If FilterByMask was used at this point, you would get the matched rows.   To delete
+the matched rows, the MatchedLineSpans must be negated (use a Pablo createNot operation).