nvtabular.ops.DifferenceLag

class nvtabular.ops.DifferenceLag(partition_cols, shift=1)

Bases: Operator

Calculates the difference between two consecutive rows of the dataset. For instance, this operator can calculate the time since a user last had another interaction.

This requires a dataset partitioned by one set of columns (userid) and sorted further by another set (userid, timestamp). The dataset must already be partitioned and sorted before being passed to the workflow. This can be easily done using dask-cudf:

# get a nvt dataset and convert to a dask dataframe
ddf = nvtabular.Dataset(PATHS).to_ddf()

# partition the dask dataframe by userid, then sort by userid/timestamp
ddf = ddf.shuffle("userid").sort_values(["userid", "timestamp"])

# create a new nvtabular dataset on the partitioned/sorted values
dataset = nvtabular.Dataset(ddf)

Once passed an appropriate dataset, this operator can be used to create a workflow to compute the lagged difference within a partition:

# compute the delta in timestamp for each users session
diff_features = ["quantity"] >> ops.DifferenceLag(partition_cols=["userid"], shift=[1, -1])
processor = nvtabular.Workflow(diff_features)

Parameters:

• partition_cols (str or list of str) – Column or Columns that are used to partition the data.

• shift (int, default 1) – The number of rows to look backwards when computing the difference lag. Negative values indicate the number of rows to look forwards, making this compute the lead instead of lag.

__init__(partition_cols, shift=1)

Methods

__init__(partition_cols[, shift])
column_mapping(col_selector)
compute_column_schema(col_name, input_schema)
compute_input_schema(root_schema, ...)	Given the schemas coming from upstream sources and a column selector for the input columns, returns a set of schemas for the input columns this operator will use
compute_output_schema(input_schema, col_selector)	Given a set of schemas and a column selector for the input columns, returns a set of schemas for the transformed columns this operator will produce
compute_selector(input_schema, selector[, ...])	Provides a hook method for sub-classes to override to implement custom column selection logic.
create_node(selector)
export(path, input_schema, output_schema, ...)	Export the class object as a config and all related files to the user defined path.
load_artifacts([artifact_path])	Load artifacts from disk required for operator function.
output_column_names(col_selector)	Given a set of columns names returns the names of the transformed columns this operator will produce
save_artifacts([artifact_path])	Save artifacts required to be reload operator state from disk
transform(col_selector, df)	Transform the dataframe by applying this operator to the set of input columns
validate_schemas(parents_schema, ...[, ...])	Provides a hook method that sub-classes can override to implement schema validation logic.

Attributes

dependencies
dynamic_dtypes
export_name	Provides a clear common english identifier for this operator.
is_subgraph
label
output_dtype
output_properties
output_tags
supported_formats
supports	Returns what kind of data representation this operator supports

transform(col_selector: ColumnSelector, df: DataFrame) → DataFrame

Transform the dataframe by applying this operator to the set of input columns

Parameters:

• col_selector (ColumnSelector) – The columns to apply this operator to

• transformable (Transformable) – A pandas or cudf dataframe that this operator will work on

Returns:

Returns a transformed dataframe or dictarray for this operator

Return type:

Transformable

property dependencies

column_mapping(col_selector)

property output_tags

property output_dtype