pyspark dataframe complex calculation with previous row - pyspark

I am working with Pyspark and trying to figure out how to do complex calculation with previous columns. I think there are generally two ways to do calculation with previous columns : Windows, and mapwithPartition. I think my problem is too complex to solve by windows, and I want the result as a sepreate row, not column. So I am trying to use mapwithpartition. I am having a trouble with syntax of this.
For instance, here is a rough draft of the code.
def change_dd(rows):
prev_rows = []
prev_rows.append(rows)
for row in rows:
new_row=[]
for entry in row:
# Testing to figure out syntax, things would get more complex
new_row.append(entry + prev_rows[0])
yield new_row
updated_rdd = select.rdd.mapPartitions(change_dd)
However, I can't access to the single data of prev_rows. Seems like prev_rows[0] is itertools.chain. How do I iterate over this prev_rows[0]?
edit
neighbor = sc.broadcast(df_sliced.where(df_sliced.id == neighbor_idx).collect()[0][:-1]).value
current = df_sliced.where(df_sliced.id == i)
def oversample_dt(dataframe):
for row in dataframe:
new_row = []
for entry, neigh in zip(row, neighbor):
if isinstance(entry, str):
if scale < 0.5:
new_row.append(entry)
else:
new_row.append(neigh)
else:
if isinstance(entry, int):
new_row.append(int(entry + (neigh - entry) * scale))
else:
new_row.append(entry + (neigh - entry) * scale)
yield new_row
sttt = time.time()
sample = current.rdd.mapPartitions(oversample_dt).toDF(schema)
In the end, I ended up doing like this for now, but I really don't want to use collect in the first row. If someone knows how to fix this / point out any problem in using pyspark, please tell me.
edit2
--Suppose Alice, and its neighbor Alice_2
scale = 0.4
+---+-------+--------+
|age| name | height |
+---+-------+--------+
| 10| Alice | 170 |
| 11|Alice_2| 175 |
+---+-------+--------+
Then, I want a row
+---+-------+----------------------------------+
|age | name | height |
+---+-------+---------------------------------+
| 10+1*0.4 | Alice_2 | 170 + 5*0.4 |
+---+-------+---------------------------------+

Why not using dataframes?
Add a column to the dataframe with the previous values using window functions like this:
from pyspark.sql import SparkSession, functions
from pyspark.sql.window import Window
spark_session = SparkSession.builder.getOrCreate()
df = spark_session.createDataFrame([{'name': 'Alice', 'age': 1}, {'name': 'Alice_2', 'age': 2}])
df.show()
+---+-------+
|age| name|
+---+-------+
| 1| Alice|
| 2|Alice_2|
+---+-------+
window = Window.partitionBy().orderBy('age')
df = df.withColumn("age-1", functions.lag(df.age).over(window))
df.show()
You can use this function for every column
+---+-------+-----+
|age| name|age-1|
+---+-------+-----+
| 1| Alice| null|
| 2|Alice_2| 1|
+---+-------+-----+
An then just make your calculus
And if you want to use rdd, then just use df.rdd

Related

transform distinct row values to different columns with corresponding rows using Pyspark

I'm new to Pyspark and trying to transform data
Given dataframe
Col1
A=id1a A=id2a B=id1b C=id1c B=id2b
D=id1d A=id3a B=id3b C=id2c
A=id4a C=id3c
Required:
A B C
id1a id1b id1c
id2a id2b id2c
id3a id3b id3b
id4a null null
I have tried pivot, but that gives first value.
There might be a better way , however an approach is splitting the column on spaces to create array of the entries and then using higher order functions(spark 2.4+) to split on the '=' for each entry in the splitted array .Then explode and create 2 columns one with the id and one with the value. Then we can assign a row number to each partition and groupby then pivot:
import pyspark.sql.functions as F
df1 = (df.withColumn("Col1",F.split(F.col("Col1"),"\s+")).withColumn("Col1",
F.explode(F.expr("transform(Col1,x->split(x,'='))")))
.select(F.col("Col1")[0].alias("cols"),F.col("Col1")[1].alias("vals")))
from pyspark.sql import Window
w = Window.partitionBy("cols").orderBy("cols")
final = (df1.withColumn("Rnum",F.row_number().over(w)).groupBy("Rnum")
.pivot("cols").agg(F.first("vals")).orderBy("Rnum"))
final.show()
+----+----+----+----+----+
|Rnum| A| B| C| D|
+----+----+----+----+----+
| 1|id1a|id1b|id1c|id1d|
| 2|id2a|id2b|id2c|null|
| 3|id3a|id3b|id3c|null|
| 4|id4a|null|null|null|
+----+----+----+----+----+
this is how df1 looks like after the transformation:
df1.show()
+----+----+
|cols|vals|
+----+----+
| A|id1a|
| A|id2a|
| B|id1b|
| C|id1c|
| B|id2b|
| D|id1d|
| A|id3a|
| B|id3b|
| C|id2c|
| A|id4a|
| C|id3c|
+----+----+
May be I don't know the full picture, but the data format seems to be strange. If nothing can be done at the data source, then some collects, pivots and joins will be needed. Try this.
import pyspark.sql.functions as F
test = sqlContext.createDataFrame([('A=id1a A=id2a B=id1b C=id1c B=id2b',1),('D=id1d A=id3a B=id3b C=id2c',2),('A=id4a C=id3c',3)],schema=['col1','id'])
tst_spl = test.withColumn("item",(F.split('col1'," ")))
tst_xpl = tst_spl.select(F.explode("item"))
tst_map = tst_xpl.withColumn("key",F.split('col','=')[0]).withColumn("value",F.split('col','=')[1]).drop('col')
#%%
tst_pivot = tst_map.groupby(F.lit(1)).pivot('key').agg(F.collect_list(('value'))).drop('1')
#%%
tst_arr = [tst_pivot.select(F.posexplode(coln)).withColumnRenamed('col',coln) for coln in tst_pivot.columns]
tst_fin = reduce(lambda df1,df2:df1.join(df2,on='pos',how='full'),tst_arr).orderBy('pos')
tst_fin.show()
+---+----+----+----+----+
|pos| A| B| C| D|
+---+----+----+----+----+
| 0|id3a|id3b|id1c|id1d|
| 1|id4a|id1b|id2c|null|
| 2|id1a|id2b|id3c|null|
| 3|id2a|null|null|null|
+---+----+----+----+----

how to loop pyspark dataframe over number of rows in dataframe

my pyspark dataframe is "Values":
+------+
|w_vote|
+------+
| 0.1|
| 0.2|
| 0.25|
| 0.3|
| 0.31|
| 0.36|
| 0.41|
| 0.5|
I want to loop to each value of a df using pyspark
My code :
out = []
for i in values.collect():
print(i)
What i basically want to do is (for (i in 1:nrow(values))
I am trying below code in pyspark but it gives result as below
Row(w_vote=0.1)
Row(w_vote=0.2)
Row(w_vote=0.25)
Row(w_vote=0.3)
Row(w_vote=0.31)
Row(w_vote=0.36)
Row(w_vote=0.41)
But i want result as 0.1, 0.2, 0.25 etc.
collect returns a Row object, which is kind of like a dict, except you access elements as attributes, not keys.
Accordingly, you can just do this:
result = [row.w_vote for row in values.collect()]
Or this:
result = [row.asDict()['w_vote'] for row in values.collect()]
As a forloop:
result = []
for row in values.collect():
result.append(row.w_vote)

Is there a better way to go about this process of trimming my spark DataFrame appropriately?

In the following example, I want to be able to only take the x Ids with the highest counts. x is number of these I want which is determined by a variable called howMany.
For the following example, given this Dataframe:
+------+--+-----+
|query |Id|count|
+------+--+-----+
|query1|11|2 |
|query1|12|1 |
|query2|13|2 |
|query2|14|1 |
|query3|13|2 |
|query4|12|1 |
|query4|11|1 |
|query5|12|1 |
|query5|11|2 |
|query5|14|1 |
|query5|13|3 |
|query6|15|2 |
|query6|16|1 |
|query7|17|1 |
|query8|18|2 |
|query8|13|3 |
|query8|12|1 |
+------+--+-----+
I would like to get the following dataframe if the variable number is 2.
+------+-------+-----+
|query |Ids |count|
+------+-------+-----+
|query1|[11,12]|2 |
|query2|[13,14]|2 |
|query3|[13] |2 |
|query4|[12,11]|1 |
|query5|[11,13]|2 |
|query6|[15,16]|2 |
|query7|[17] |1 |
|query8|[18,13]|2 |
+------+-------+-----+
I then want to remove the count column, but that is trivial.
I have a way to do this, but I think it defeats the purpose of scala all together and completely wastes a lot of runtime. Being new, I am unsure about the best ways to go about this
My current method is to first get a distinct list of the query column and create an iterator. Second I loop through the list using the iterator and trim the dataframe to only the current query in the list using df.select($"eachColumnName"...).where("query".equalTo(iter.next())). I then .limit(howMany) and then groupBy($"query").agg(collect_list($"Id").as("Ids")). Lastly, I have an empty dataframe and add each of these one by one to the empty dataframe and return this newly created dataframe.
df.select($"query").distinct().rdd.map(r => r(0).asInstanceOf[String]).collect().toList
val iter = queries.toIterator
while (iter.hasNext) {
middleDF = df.select($"query", $"Id", $"count").where($"query".equalTo(iter.next()))
queryDF = middleDF.sort(col("count").desc).limit(howMany).select(col("query"), col("Ids")).groupBy(col("query")).agg(collect_list("Id").as("Ids"))
emptyDF.union(queryDF) // Assuming emptyDF is made
}
emptyDF
I would do this using Window-Functions to get the rank, then groupBy to aggrgate:
import org.apache.spark.sql.expressions.Window
import org.apache.spark.sql.functions._
val howMany = 2
val newDF = df
.withColumn("rank",row_number().over(Window.partitionBy($"query").orderBy($"count".desc)))
.where($"rank"<=howMany)
.groupBy($"query")
.agg(
collect_list($"Id").as("Ids"),
max($"count").as("count")
)

List to DataFrame in pyspark

Can someone tell me how to convert a list containing strings to a Dataframe in pyspark. I am using python 3.6 with spark 2.2.1. I am just started learning spark environment and my data looks like below
my_data =[['apple','ball','ballon'],['cat','camel','james'],['none','focus','cake']]
Now, i want to create a Dataframe as follows
---------------------------------
|ID | words |
---------------------------------
1 | ['apple','ball','ballon'] |
2 | ['cat','camel','james'] |
I even want to add ID column which is not associated in the data
You can convert the list to a list of Row objects, then use spark.createDataFrame which will infer the schema from your data:
from pyspark.sql import Row
R = Row('ID', 'words')
# use enumerate to add the ID column
spark.createDataFrame([R(i, x) for i, x in enumerate(my_data)]).show()
+---+--------------------+
| ID| words|
+---+--------------------+
| 0|[apple, ball, bal...|
| 1| [cat, camel, james]|
| 2| [none, focus, cake]|
+---+--------------------+
Try this -
data_array = []
for i in range (0,len(my_data)) :
data_array.extend([(i, my_data[i])])
df = spark.createDataframe(data = data_array, schema = ["ID", "words"])
df.show()
Try this -- the simplest approach
from pyspark.sql import *
x = Row(utc_timestamp=utc, routine='routine name', message='your message')
data = [x]
df = sqlContext.createDataFrame(data)
Simple Approach:
my_data =[['apple','ball','ballon'],['cat','camel','james'],['none','focus','cake']]
spark.sparkContext.parallelize(my_data).zipWithIndex() \
toDF(["id", "words"]).show(truncate=False)
+---------------------+-----+
|id |words|
+---------------------+-----+
|[apple, ball, ballon]|0 |
|[cat, camel, james] |1 |
|[none, focus, cake] |2 |
+---------------------+-----+

How to randomly selecting rows from one dataframeusing information from another dataframe

The following I am attempting in Scala-Spark.
I'm hoping someone can give me some guidance on how to tackle this problem or provide me with some resources to figure out what I can do.
I have a dateCountDF with a count corresponding to a date. I would like to randomly select a certain number of entries for each dateCountDF.month from another Dataframe entitiesDF where dateCountDF.FirstDate<entitiesDF.Date && entitiesDF.Date <= dateCountDF.LastDate and then place all the results into a new Dataframe. See Bellow for Data Example
I'm not at all sure how to approach this problem from a Spark-SQl or Spark-MapReduce perspective. The furthest I got was the naive approach, where I use a foreach on a dataFrame and then refer to the other dataframe within the function. But this doesn't work because of the distributed nature of Spark.
val randomEntites = dateCountDF.foreach(x => {
val count:Int = x(1).toString().toInt
val result = entitiesDF.take(count)
return result
})
DataFrames
**dateCountDF**
| Date | Count |
+----------+----------------+
|2016-08-31| 4|
|2015-12-31| 1|
|2016-09-30| 5|
|2016-04-30| 5|
|2015-11-30| 3|
|2016-05-31| 7|
|2016-11-30| 2|
|2016-07-31| 5|
|2016-12-31| 9|
|2014-06-30| 4|
+----------+----------------+
only showing top 10 rows
**entitiesDF**
| ID | FirstDate | LastDate |
+----------+-----------------+----------+
| 296| 2014-09-01|2015-07-31|
| 125| 2015-10-01|2016-12-31|
| 124| 2014-08-01|2015-03-31|
| 447| 2017-02-01|2017-01-01|
| 307| 2015-01-01|2015-04-30|
| 574| 2016-01-01|2017-01-31|
| 613| 2016-04-01|2017-02-01|
| 169| 2009-08-23|2016-11-30|
| 205| 2017-02-01|2017-02-01|
| 433| 2015-03-01|2015-10-31|
+----------+-----------------+----------+
only showing top 10 rows
Edit:
For clarification.
My inputs are entitiesDF and dateCountDF. I want to loop through dateCountDF and for each row I want to select a random number of entities in entitiesDF where dateCountDF.FirstDate<entitiesDF.Date && entitiesDF.Date <= dateCountDF.LastDate
To select random you do like this in scala
import random
def sampler(df, col, records):
# Calculate number of rows
colmax = df.count()
# Create random sample from range
vals = random.sample(range(1, colmax), records)
# Use 'vals' to filter DataFrame using 'isin'
return df.filter(df[col].isin(vals))
select random number of rows you want store in dataframe and the add this data in the another dataframe for this you can use unionAll.
also you can refer this answer