我正在使用pySpark
,并设置了我的数据框,其中两列代表每日资产价格,如下所示:
ind = sc.parallelize(range(1,5))
prices = sc.parallelize([33.3,31.1,51.2,21.3])
data = ind.zip(prices)
df = sqlCtx.createDataFrame(data,["day","price"])
我开始申请df.show()
:
+---+-----+
|day|price|
+---+-----+
| 1| 33.3|
| 2| 31.1|
| 3| 51.2|
| 4| 21.3|
+---+-----+
哪个好,一切都好。我想有另一个专栏,其中包含价格列的日常回报,即类似的内容
(price(day2)-price(day1))/(price(day1))
经过大量研究后,我被告知通过应用pyspark.sql.window
函数可以最有效地完成,但我无法看到如何。
您可以使用lag函数带来前一天的列,并添加从两列执行实际日常返回的其他列,但您可能必须告诉spark如何对数据进行分区和/或命令它执行滞后操作,像这样:
from pyspark.sql.window import Window
import pyspark.sql.functions as func
from pyspark.sql.functions import lit
dfu = df.withColumn('user', lit('tmoore'))
df_lag = dfu.withColumn('prev_day_price',
func.lag(dfu['price'])
.over(Window.partitionBy("user")))
result = df_lag.withColumn('daily_return',
(df_lag['price'] - df_lag['prev_day_price']) / df_lag['price'] )
>>> result.show()
+---+-----+-------+--------------+--------------------+
|day|price| user|prev_day_price| daily_return|
+---+-----+-------+--------------+--------------------+
| 1| 33.3| tmoore| null| null|
| 2| 31.1| tmoore| 33.3|-0.07073954983922816|
| 3| 51.2| tmoore| 31.1| 0.392578125|
| 4| 21.3| tmoore| 51.2| -1.403755868544601|
+---+-----+-------+--------------+--------------------+
这里有更长的介绍Window functions in Spark。
滞后功能可以帮助您解决用例。
from pyspark.sql.window import Window
import pyspark.sql.functions as func
### Defining the window
Windowspec=Window.orderBy("day")
### Calculating lag of price at each day level
prev_day_price= df.withColumn('prev_day_price',
func.lag(dfu['price'])
.over(Windowspec))
### Calculating the average
result = prev_day_price.withColumn('daily_return',
(prev_day_price['price'] - prev_day_price['prev_day_price']) /
prev_day_price['price'] )