class_docstr: Abstract class for business days since a previous event.
  Returns the number of **business days** (not trading days!) since
  the most recent event date for each asset.
  
  This doesn't use trading days for symmetry with
  BusinessDaysUntilNextEarnings.
  
  Assets which announced or will announce the event today will produce a
  value of 0.0. Assets that announced the event on the previous business
  day will produce a value of 1.0.
  
  Assets for which the event date is `NaT` will produce a value of `NaN`.
  
  
  Example
  -------
  ``BusinessDaysSincePreviousEvent`` can be used to create an event-driven
  factor. For instance, you may want to only trade assets that have
  a data point with an asof_date in the last 5 business days. To do this,
  you can create a ``BusinessDaysSincePreviousEvent`` factor, supplying
  the relevant asof_date column from your dataset as input, like this::
  
      # Factor computing number of days since most recent asof_date
      # per asset.
      days_since_event = BusinessDaysSincePreviousEvent(
          inputs=[MyDataset.asof_date]
      )
  
      # Filter returning True for each asset whose most recent asof_date
      # was in the last 5 business days.
      recency_filter = (days_since_event <= 5)
code: def _compute(self, arrays, dates, assets, mask):
      # Coerce from [ns] to [D] for numpy busday_count.
      announce_dates = arrays[0].astype(datetime64D_dtype)
  
      # Set masked values to NaT.
      announce_dates[~mask] = NaTD
  
      # Convert row labels into a column vector for broadcasted comparison.
      reference_dates = dates.values.astype(datetime64D_dtype)[
          :, newaxis
      ]
      return busday_count_mask_NaT(announce_dates, reference_dates)
  
file_path: zipline/zipline/pipeline/factors/events.py
imports: from numpy import newaxis
  from zipline.utils.numpy_utils import NaTD, busday_count_mask_NaT, datetime64D_dtype, float64_dtype
  from .factor import Factor
label_desc: Use image node_id 1 for calling the BusinessDaysSincePreviousEvent obj's underlying member method code with example usage: obj._compute(arrays, dates, assets, mask) and returns: busday_count_mask_NaT