Dataframe, part deux - add varData and summarize() (#608)

* initial dataframe commit

* initial dataframe port of core app

* rename variables for clarity

* remove unused import

* comment out unused code

* fix array handling bug in crossfilter dimension creation

* allow creation of empty dataframes

* handle non-existent columns

* handle non-existent columns

* revise tests for new dataframe

* comments for clarity

* comments for clarity

* generate bulk add placeholder with real gene names

* fix bug in gene name adding

* more dataframe unit tests

* fix bug - subset from current world, not universe

* put cut and pasted code into a single function

* improve caching of crossfilter

* remove cascading update bug from graph

* more performance work

* improve state handling for scatterplot

* performance optimization of critical path

* add column summarization

* dataframe utils

* add callOnceLazy

* fix tests

* minor updates found during review

* fix misspelling

* remove RESTv02 from function names

* comment cleanup

* cut/icut col parameter defaults to null

* break up large test

* improve tests and comments on dataframe at/has functions

* add Dataframe withCol/dropCol

* expression varData now stored in a dataframe

* dead code cleanup

* use dataframe.summarize()

* test cases for Dataframe.col.summarize

* update test cases for new dataframe summarize

* improve naming

* use new hasCol API

* add comments

* add more Dataframe.withCol tests

* add ability to specify row index in cut operation

* retire subsetVarData function

* correctly handle expression subsetting

* lint and improve comments

* rename cut to subset

* changes based on PR review

client/src/components/geneExpression/cellSetButtons.js

@@ -14,7 +14,11 @@ class CellSetButton extends React.Component {
       eitherCellSetOneOrTwo
     } = this.props;
 
-    const set = World.getSelectedByIndex(crossfilter);
+    // Reducer and components assume that value will be null if
+    // no selection made.  World..getSelectedByIndex() returns a
+    // zero length TypedArray when nothing is selected.
+    let set = World.getSelectedByIndex(crossfilter);
+    if (set.length === 0) set = null;
 
     if (!differential.diffExp) {
       /* diffexp needs to be cleared before we store a new set */