Pyspark : forward fill with last observation for a DataFrame

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Another workaround to get this working, is to try something like this:

from pyspark.sql import functions as F
from pyspark.sql.window import Window

window = (
    Window
    .partitionBy('cookie_id')
    .orderBy('Time')
    .rowsBetween(Window.unboundedPreceding, Window.currentRow)
)

final = (
    joined
    .withColumn('UserIDFilled', F.last('User_ID', ignorenulls=True).over(window))
)

So what this is doing is that it constructs your window based on the partition key and the order column. It also tells the window to look back all rows within the window up to the current row. Finally, at each row, you return the last value that is not null (which remember, according to your window, it includes your current row)

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