* add appending utility
* add appending utility
* update comment
* rename to mutable
* move mutable functions out of DataFrameHelper
* move mutable functions out of DataFrameHelper
* move mutable functions out of DataFrameHelper
* turn DataFrameHelper into FieldCache
* guess time from name
* graph the numbers
* return the timeField, not just the index
* just warn on duplicate field names
* only use a parser if the input is a string
* append init all fields to the same length
* typo
* only parse string if value is a string
* DataFrame: test fixes
* Switch to null for missing values
* Fixed tests
