React Native renderSectionHeader example

format.js

//First put this in your constructor function:
var getSectionData = (dataBlob, sectionID) => {
  return dataBlob[sectionID];
}
var getRowData = (dataBlob, sectionID, rowID) => {
  return dataBlob[sectionID + ':' + rowID];
}
this.ds = new ListView.DataSource({
  getSectionData: getSectionData,
  getRowData: getRowData,
  rowHasChanged: (r1, r2) => r1 !== r2,
  sectionHeaderHasChanged: (s1, s2) => s1 !== s2
})  

//Then you have to create a dataBlob object, an array of sectionIDs, and an array of rowID arrays with the following formats:
var dataBlob = {
  'sectionID1' : { ...section1 data },
  'sectionID1:rowID1' : { ...row1 data },
  'sectionID1:rowID2' : { ..row2 data },
  'sectionID2' : { ...section2 data },
  'sectionID2:rowID1' : { ...row1 data },
  'sectionID2:rowID2' : { ..row2 data },
  ...
}

var sectionIDs = [ 'sectionID1', 'sectionID2', ... ]

var rowIDs = [ [ 'rowID1', 'rowID2' ], [ 'rowID1', 'rowID2' ], ... ]

//Finally, you can create a valid dataSource for your list with:
this.ds.cloneWithRowsAndSections(dataBlob, sectionIDs, rowIDs)

//Hope this helps someone else.