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https://issues.apache.org/jira/browse/SPARK-20357?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jeeyoung Kim updated SPARK-20357:
---------------------------------
Affects Version/s: 2.1.0
> Expose Calendar.getWeekYear() as Spark SQL date function to be consistent
> with weekofyear()
> -------------------------------------------------------------------------------------------
>
> Key: SPARK-20357
> URL: https://issues.apache.org/jira/browse/SPARK-20357
> Project: Spark
> Issue Type: New Feature
> Components: SQL
> Affects Versions: 2.1.0, 2.2.0
> Reporter: Jeeyoung Kim
> Priority: Minor
>
> Since weeks and years are extracted using different boundaries (weeks happen
> every 7 days, years happen every 365-ish days, which is not divisible by 7),
> there are weird inconsistencies around how end-of-the year dates are handled
> if you use {{year}} and {{weekofyear}} Spark SQL functions. The example below
> shows how "2016-01-01" and "2016-12-30" has the same {{(year, week)}} pair.
> This happens because the week for "2016-01-01" is calculated as "last week of
> 2015". the Year function in Spark SQL ignores this and returns YYYY component
> of YYYY-MM-DD.
> The correct way to fix this is by exposing {{Java.util.dates.getWeekYear}}.
> This function calculates week-based years, so "2016-01-01" will return 2015
> instead. in this case.
> {noformat}
> # Trying out the bug for date - using PySpark
> import pyspark.sql.functions as F
> df = spark.createDataFrame([("2016-12-31",),("2016-12-30",), ("2017-01-01",),
> ("2017-01-02",),("2017-12-30",)], ['id'])
> df_parsed = (
> df
> .withColumn("year", F.year(df['id'].cast("date")))
> .withColumn("weekofyear", F.weekofyear(df['id'].cast("date")))
> )
> df_parsed.show()
> {noformat}
> Prints
> {noformat}
> +----------+----+----------+
> | id|year|weekofyear|
> +----------+----+----------+
> |2016-12-31|2016| 52|
> |2016-12-30|2016| 52|
> |2017-01-01|2017| 52| <- same (year, weekofyear) output
> |2017-01-02|2017| 1|
> |2017-12-30|2017| 52| <-
> +----------+----+----------+
> {noformat}
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