public void addInitialColumn(String columnName) {
    initialColumnNames.add(columnName);
    int index = projectedColumns.size();
    projectedColumns.add(index);
    projectionColumnNames.add(columnName);
    projectionColumnMap.put(columnName, index);
  }
Context class for vectorization execution.
Main role is to map column names to column indices and serves as a
factory class for building vectorized expressions out of descriptors.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java