A placeholder value is a deliberate substitute used when the original value cannot be directly handled in the required format or operation. It preserves the record while making a conversion, grouping, filter, or aggregation possible. The substitute must remain distinguishable from genuine data. section 5.4.3 section 8.4.1
Choose a value that cannot be mistaken for an observed one. For numeric fields, inspect the range first: negative values can stand in for missing link lengths only after confirming that negatives do not occur. For text fields, use an explicit label such as “PLACEHOLDER,” then restore missing values after grouping when the placeholder was only needed for processing. section 8.4.1
Making censored revenue numeric
A gross box-office value of “<0.1” cannot be converted directly to a number and is neither zero nor 0.1. Replacing it with 0.05 represents low revenue, permits numeric conversion, and enables revenue totals by genre and year. section 5.4.3
Keeping missing street names filterable
When a street name is absent but records should remain available to an app, filling the field with “-- NO STREET INFORMATION --” creates a clear value that users can filter on. section 10.4.1
genres.loc[genres["Gross box office (£ million)"] == "<0.1", "Gross box office (£ million)"] = 0.05 genres["Gross box office (£ million)"] = genres["Gross box office (£ million)"].astype(float)
This transformation replaces the censored revenue marker before casting the column to floating point. section 5.4.3
