# Lazy Dataframes Refactor

All commands listed were either commands modified to be lazy only, or eager commands that I did not change.

When commands are not changed it is because:
* The operation is not available in a lazy form
* The operation requires that the dataframe be collected

## Type conversion
Removed all the automatic eager/lazy type conversion code. If a command is lazy only, the dataframe will still be converted to a lazy frame if it is an eager. For the remaining eager commands, lazy dataframes will be converted to eager dataframes.

## append
**STATUS:** UNMODIFIED
This command will require collecting a lazy frame.. perhaps leave as an eager dataframe?

## cast
**STATUS:** modified
This command can be changed to just convert a dataframe from a lazy frame and handle both as lazy

## columns
**STATUS:** UNMODIFIED
This command requires collecting a dataframe.

## drop
**STATUS:** modified
Re-implemented to be lazy

## drop-duplicates
**STATUS:** modified
Re-implemented to be lazy

## drop-nulls
**STATUS:** MODIFIED
Re-implemented to be lazy

## dummies
**STATUS:** UNMODIFIED
This operation only works with eager dataframes

## filter-with
**STATUS:** MODIFIED
Re-implemented to be lazy only. Filter must be applied with an expression. Using a Dataframe mask is nolonger supported.

## first
**STATUS:** MODIFIED
re-implemented to be lazy of expression

## query
**STATUS:** UNMODIFIED

## last
**STATUS:** MODIFIED
re-implemented to be lazy of expression. Changed the behavior to more closely work like the nu last command by only returning 1 row when called without a number of rows.

## shape
**STATUS:** UNMODIFIED

## melt
**STATUS:** MODIFIED
Re-implemented to be lazy

## slice
**STATUS:** MODIFIED
Re-implemented to be lazy

## take
**STATUS:** UNMODIFIED
No equivalent lazy functionality

## open
**STATUS:** MODIFIED
All file types that support the ability to create lazy frames now return lazy frames. The `--lazy` flag has been removed.

### Returns lazy dataframe

* parquet
* json lines
* ipc / arrow
* CSV

### Return eager dataframe

* json
* avro

## unique
**STATUS:** MODIFIED
Changed to work with only lazy

## to-lazy
**STATUS:** REMOVED
The command is now redundant. All operations that work with lazy frames will automatically convert the eager frame to a lazy frame.

## to-<file format>
**STATUS:** UNMODIFIED
All of these commands require that the data be collected before writing anyway.