I am trying to create multiple columns dynamically based on filter condition after comparing two data frame with below code
source_df
+---+-----+-----+----+
|key|val11|val12|date|
+---+-----+-----+-----+
|abc| 1.1| john|2-3-21
|def| 3.0| dani|2-2-21
+---+-----+-----+------
dest_df
+---+-----+-----+------+
|key|val11|val12|date |
+---+-----+-----+------
|abc| 2.1| jack|2-3-21|
|def| 3.0| dani|2-2-21|
-----------------------
columns= source_df.columns[1:]
joined_df=source_df\
.join(dest_df, 'key', 'full')
for column in columns:
column_name="difference_in_"+str(column)
report = joined_df\
.filter((source_df[column] != dest_df[column]))\
.withColumn(column_name, F.concat(F.lit('[src:'), source_df[column], F.lit(',dst:'),dest_df[column],F.lit(']')))
The output I expect is
#Expected
+---+-----------------+------------------+
|key| difference_in_val11| difference_in_val12 |
+---+-----------------+------------------+
|abc|[src:1.1,dst:2.1]|[src:john,dst:jack]|
+---+-----------------+-------------------+
I get only one column result
#Actual
+---+-----------------+-
|key| difference_in_val12 |
+---+-----------------+-|
|abc|[src:john,dst:jack]|
+---+-----------------+-
How to generate multiple columns based on filter condition dynamically?
Dataframes are immutable objects. Having said that, you need to create another dataframe using the one that got generated in the 1st iteration. Something like below -
from pyspark.sql import functions as F
columns= source_df.columns[1:]
joined_df=source_df\
.join(dest_df, 'key', 'full')
for column in columns:
if column != columns[-1]:
column_name="difference_in_"+str(column)
report = joined_df\
.filter((source_df[column] != dest_df[column]))\
.withColumn(column_name, F.concat(F.lit('[src:'), source_df[column], F.lit(',dst:'),dest_df[column],F.lit(']')))
else:
column_name="difference_in_"+str(column)
report1 = report.filter((source_df[column] != dest_df[column]))\
.withColumn(column_name, F.concat(F.lit('[src:'), source_df[column], F.lit(',dst:'),dest_df[column],F.lit(']')))
report1.show()
#report.show()
Output -
+---+-----+-----+-----+-----+-------------------+-------------------+
|key|val11|val12|val11|val12|difference_in_val11|difference_in_val12|
+---+-----+-----+-----+-----+-------------------+-------------------+
|abc| 1.1| john| 2.1| jack| [src:1.1,dst:2.1]|[src:john,dst:jack]|
+---+-----+-----+-----+-----+-------------------+-------------------+
You could also do this with a union of both dataframes and then collect list only if collect_set size is greater than 1 , this can avoid joining the dataframes:
from pyspark.sql import functions as F
cols = source_df.drop("key").columns
output = (source_df.withColumn("ref",F.lit("src:"))
.unionByName(dest_df.withColumn("ref",F.lit("dst:"))).groupBy("key")
.agg(*[F.when(F.size(F.collect_set(i))>1,F.collect_list(F.concat("ref",i))).alias(i)
for i in cols]).dropna(subset = cols, how='all')
)
output.show()
+---+------------------+--------------------+
|key| val11| val12|
+---+------------------+--------------------+
|abc|[src:1.1, dst:2.1]|[src:john, dst:jack]|
+---+------------------+--------------------+
Related
I have the below dataframe which I have read from a JSON file.
1
2
3
4
{"todo":["wakeup", "shower"]}
{"todo":["brush", "eat"]}
{"todo":["read", "write"]}
{"todo":["sleep", "snooze"]}
I need my output to be as below Key and Value. How do I do this? Do I need to create a schema?
ID
todo
1
wakeup, shower
2
brush, eat
3
read, write
4
sleep, snooze
The key-value which you refer to is a struct. "keys" are struct field names, while "values" are field values.
What you want to do is called unpivoting. One of the ways to do it in PySpark is using stack. The following is a dynamic approach, where you don't need to provide existent column names.
Input dataframe:
df = spark.createDataFrame(
[((['wakeup', 'shower'],),(['brush', 'eat'],),(['read', 'write'],),(['sleep', 'snooze'],))],
'`1` struct<todo:array<string>>, `2` struct<todo:array<string>>, `3` struct<todo:array<string>>, `4` struct<todo:array<string>>')
Script:
to_melt = [f"\'{c}\', `{c}`.todo" for c in df.columns]
df = df.selectExpr(f"stack({len(to_melt)}, {','.join(to_melt)}) (ID, todo)")
df.show()
# +---+----------------+
# | ID| todo|
# +---+----------------+
# | 1|[wakeup, shower]|
# | 2| [brush, eat]|
# | 3| [read, write]|
# | 4| [sleep, snooze]|
# +---+----------------+
Use from_json to convert string to array. Explode to cascade each unique element to row.
data
df = spark.createDataFrame(
[(('{"todo":"[wakeup, shower]"}'),('{"todo":"[brush, eat]"}'),('{"todo":"[read, write]"}'),('{"todo":"[sleep, snooze]"}'))],
('value1','values2','value3','value4'))
code
new = (df.withColumn('todo', explode(flatten(array(*[map_values(from_json(x, "MAP<STRING,STRING>")) for x in df.columns])))) #From string to array to indivicual row
.withColumn('todo', translate('todo',"[]",'')#Remove corner brackets
) ).show(truncate=False)
outcome
+---------------------------+-----------------------+------------------------+--------------------------+--------------+
|value1 |values2 |value3 |value4 |todo |
+---------------------------+-----------------------+------------------------+--------------------------+--------------+
|{"todo":"[wakeup, shower]"}|{"todo":"[brush, eat]"}|{"todo":"[read, write]"}|{"todo":"[sleep, snooze]"}|wakeup, shower|
|{"todo":"[wakeup, shower]"}|{"todo":"[brush, eat]"}|{"todo":"[read, write]"}|{"todo":"[sleep, snooze]"}|brush, eat |
|{"todo":"[wakeup, shower]"}|{"todo":"[brush, eat]"}|{"todo":"[read, write]"}|{"todo":"[sleep, snooze]"}|read, write |
|{"todo":"[wakeup, shower]"}|{"todo":"[brush, eat]"}|{"todo":"[read, write]"}|{"todo":"[sleep, snooze]"}|sleep, snooze |
+---------------------------+-----------------------+------------------------+--------------------------+--------------+
I have one dataframe - df_similar_strings, which looks like this:
|---------------------|
| string_values |
|---------------------|
| ['catish', 'cat'] |
|---------------------|
| ['doggo', 'dogy'] |
|---------------------|
and the other one - df_source:
|-----------------------------|------------------|
| values | key_value |
|-----------------------------|------------------|
| ['catish', 'cat', 'cat-'] | cat |
|-----------------------------|------------------|
| ['doggo', 'dogy', 'dog'] | dog |
|-----------------------------|------------------|
I would like to join those data frames based on the column string_values and values so that there is at least one value matching.
I have no idea how to do this since the columns are nested as arrays.
Hey you just need to type cast your list to tuple. And then try merging. Since list is unhashable hence merge operation can't be applied. Try this
df_source.values = df_source["values"].apply(lambda x: tuple(x))
Similarly with the other df and try merging using pd merge.
You can solve it by first doing a cartesian-product between your two dataframes and then dropping from that dataframe all rows which doesn't have any shared value.
For simplicity, I assume the columns on both datasets have the same name ("values"). Also, I assume the lists doesn't have repeated values (all values appear once).
from collections import Counter
def find_duplicates(arr):
return [item for item,count in Counter(arr).items() if count==2]
df1['key']=1
df2['key']=1
cartes_prod_df = df1.merge(df2,on=['key'],how='outer').drop(columns=['key'])
duplicate_values = (cartes_prod_df.values_x + cartes_prod_df.values_y).apply(find_duplicates)
merged_df = cartes_prod_df[duplicate_values.apply(lambda x: len(x)>0)]
I've used a little trick in order to do the cartesian product (Adding the key column), and then the duplicate_values found from the joint array (using the + operator) are the values which appeared twice in the joint array.
UPDATE
In order to supply a full example, here's an example of df1 and df2:
d1 = {'values': [['A','B'],['B','C'],['D']],'otherkey':[1,2,3]}
d2 = {'values': [['A'],['B'],['A','C'],['D']],'otherkey':[4,5,3,6]}
df1 = pd.DataFrame(d1)
df2 = pd.DataFrame(d2)
Now, merged_df would give the output:
I have a dataframe which looks like one given below. All the values for a corresponding id is the same except for the mappingcol field.
+--------------------+----------------+--------------------+-------+
|misc |fruit |mappingcol |id |
+--------------------+----------------+--------------------+-------+
|ddd |apple |Map("name"->"Sameer"| 1 |
|ref |banana |Map("name"->"Riyazi"| 2 |
|ref |banana |Map("lname"->"Nikki"| 2 |
|ddd |apple |Map("lname"->"tenka"| 1 |
+--------------------+----------------+--------------------+-------+
I want to merge the rows with same row in such a way that I get exactly one row for one id and the value of mappingcol needs to be merged. The output should look like :
+--------------------+----------------+--------------------+-------+
|misc |fruit |mappingcol |id |
+--------------------+----------------+--------------------+-------+
|ddd |apple |Map("name"->"Sameer"| 1 |
|ref |banana |Map("name"->"Riyazi"| 2 |
+--------------------+----------------+--------------------+-------+
the value for mappingcol for id = 1 would be :
Map(
"name" -> "Sameer",
"lname" -> "tenka"
)
I know that maps can be merged using ++ operator, so thats not what im worried about. I just cant understand how to merge the rows, because if I use a groupBy, I have nothing to aggregate the rows on.
You can use by groupBy and then managing a little the map
df.groupBy("id", "fruit", "misc").agg(collect_list("mappingcol"))
.as[(Int, String, String, Seq[Map[String, String]])]
.map { case (id, fruit, misc, list) => (id, fruit, misc, list.reduce(_ ++ _)) }
.toDF("id", "fruit", "misc", "mappingColumn")
With the first line, tou group by your desired columns and aggregate the map pairs in the same element (an array)
With the second line (as), you convert your structure to a Dataset of a Tuple4 with the last element being a sequence of maps
With the third line (map), you merge all the elements to a single map
With the last line (toDF) to give the columns the original names
OUTPUT
+---+------+----+--------------------------------+
|id |fruit |misc|mappingColumn |
+---+------+----+--------------------------------+
|1 |apple |ddd |[name -> Sameer, lname -> tenka]|
|2 |banana|ref |[name -> Riyazi, lname -> Nikki]|
+---+------+----+--------------------------------+
You can definitely do the above with a Window function!
This is in PySpark not Scala but there's almost no difference when only using native Spark functions.
The below code only works on a map column that 1 one key, value pair per row, as it how your example data is, but it can be made to work with map columns with multiple entries.
from pyspark.sql import Window
map_col = 'mappingColumn'
group_cols = ['id', 'fruit', 'misc']
# or, a lazier way if you have a lot of columns to group on
cols = df.columns # save as list
group_cols_2 = cols.remove('mappingCol') # remove what you're not grouping by
w = Window.partitionBy(group_cols)
# unpack map value and key into a pair struct column
df1 = df.withColumn(map_col , F.struct(F.map_keys(map_col)[0], F.map_values(map_col)[0]))
# Collect all key values into an array of structs, here each row
# contains the map entries for all rows in the group/window
df1 = df1.withColumn(map_col , F.collect_list(map_col).over(w))
# drop duplicate values, as you only want one row per group
df1 = df1.dropDuplicates(group_cols)
# return the values for map type
df1 = df1.withColumn(map_col , F.map_from_entries(map_col))
You can save the output of each step to a new column to see how each step works, as I have done below.
from pyspark.sql import Window
map_col = 'mappingColumn'
group_cols = list('id', 'fruit', 'misc')
w = Window.partitionBy(group_cols)
df1 = df.withColumn('test', F.struct(F.map_keys(map_col)[0], F.map_values(map_col)[0]))
df1 = df1.withColumn('test1', F.collect_list('test').over(w))
df1 = df1.withColumn('test2', F.map_from_entries('test1'))
df1.show(truncate=False)
df1.printSchema()
df1 = df1.dropDuplicates(group_cols)
I have a spark dataframe (12m x 132) and I am trying to calculate the number of unique values by column, and remove columns that have only 1 unique value.
So far, I have used the pandas nunique function as such:
import pandas as pd
df = sql_dw.read_table(<table>)
df_p = df.toPandas()
nun = df_p.nunique(axis=0)
nundf = pd.DataFrame({'atr':nun.index, 'countU':nun.values})
dropped = []
for i, j in nundf.values:
if j == 1:
dropped.append(i)
df = df.drop(i)
print(dropped)
Is there a way to do this that is more native to spark - i.e. not using pandas?
Please have a look at the commented example below. The solution requires more python as pyspark specific knowledge.
import pyspark.sql.functions as F
#creating a dataframe
columns = ['asin' ,'ctx' ,'fo' ]
l = [('ASIN1','CTX1','FO1')
,('ASIN1','CTX1','FO1')
,('ASIN1','CTX1','FO2')
,('ASIN1','CTX2','FO1')
,('ASIN1','CTX2','FO2')
,('ASIN1','CTX2','FO2')
,('ASIN1','CTX2','FO3')
,('ASIN1','CTX3','FO1')
,('ASIN1','CTX3','FO3')]
df=spark.createDataFrame(l, columns)
df.show()
#we create a list of functions we want to apply
#in this case countDistinct for each column
expr = [F.countDistinct(c).alias(c) for c in df.columns]
#we apply those functions
countdf = df.select(*expr)
#this df has just one row
countdf.show()
#we extract the columns which have just one value
cols2drop = [k for k,v in countdf.collect()[0].asDict().items() if v == 1]
df.drop(*cols2drop).show()
Output:
+-----+----+---+
| asin| ctx| fo|
+-----+----+---+
|ASIN1|CTX1|FO1|
|ASIN1|CTX1|FO1|
|ASIN1|CTX1|FO2|
|ASIN1|CTX2|FO1|
|ASIN1|CTX2|FO2|
|ASIN1|CTX2|FO2|
|ASIN1|CTX2|FO3|
|ASIN1|CTX3|FO1|
|ASIN1|CTX3|FO3|
+-----+----+---+
+----+---+---+
|asin|ctx| fo|
+----+---+---+
| 1| 3| 3|
+----+---+---+
+----+---+
| ctx| fo|
+----+---+
|CTX1|FO1|
|CTX1|FO1|
|CTX1|FO2|
|CTX2|FO1|
|CTX2|FO2|
|CTX2|FO2|
|CTX2|FO3|
|CTX3|FO1|
|CTX3|FO3|
+----+---+
My apologies as I don't have the solution in pyspark but in pure spark, which may be transferable or used in case you can't find a pyspark way.
You can create a blank list and then using a foreach, check which columns have a distinct count of 1, then append them to the blank list.
From there you can use the list as a filter and drop those columns from your dataframe.
var list_of_columns: List[String] = ()
df_p.columns.foreach{c =>
if (df_p.select(c).distinct.count == 1)
list_of_columns ++= List(c)
df_p_new = df_p.drop(list_of_columns:_*)
you can group your df by that column and count distinct value of this column:
df = df.groupBy("column_name").agg(countDistinct("column_name").alias("distinct_count"))
And then filter your df by row which has more than 1 distinct_count:
df = df.filter(df.distinct_count > 1)
is there any way to create/fill columns with pyspark 2.1.0 where the name of the column is the value of a different column?
I tried the following
def createNewColumnsFromValues(dataFrame, colName, targetColName):
"""
Set value of column colName to targetColName's value
"""
cols = dataFrame.columns
#df = dataFrame.withColumn(f.col(colName), f.col(targetColName))
df = dataFrame.withColumn('x', f.col(targetColName))
return df
The out commented line does not work, when calling the method I get the error
TypeError: 'Column' object is not callable
whereas the fixed name (as a string) is no problem. Any idea of how to also make the name of the column come from another one, not just the value? I also tried to use a UDF function definition as a workaround with the same no success result.
Thanks for help!
Edit:
from pyspark.sql import functions as f
I figured a solution which scales nicely for few (or not many) distinct values I need columns for. Which is necessarily the case or the number of columns would explode.
def createNewColumnsFromValues(dataFrame, colName, targetCol):
distinctValues = dataFrame.select(colName).distinct().collect()
for value in distinctValues:
dataFrame = dataFrame.withColumn(str(value[0]), f.when(f.col(colName) == value[0], f.col(targetCol)).otherwise(f.lit(None)))
return dataFrame
You might want to try the following code:
test_df = spark.createDataFrame([
(1,"2",5,1),(3,"4",7,8),
], ("col1","col2","col3","col4"))
def createNewColumnsFromValues(dataFrame, sourceCol, colName, targetCol):
"""
Set value column colName to targetCol
"""
for value in sourceCol:
dataFrame = dataFrame.withColumn(str(value[0]), when(col(colName)==value[0], targetCol).otherwise(None))
return dataFrame
createNewColumnsFromValues(test_df, test_df.select("col4").collect(), "col4", test_df["col3"]).show()
The trick here is to do select("COLUMNNAME").collect() to get a list of the values in the column. Then colName contains this list, which is a list of rows, where each row has a single element. So you can directly iterate through the list and access the element at position 0. In this case a cast to string was necessary to ensure the column name of the new column is a string. The target column is used for the values for each of the individual columns. So the result would look like:
+----+----+----+----+----+----+
|col1|col2|col3|col4| 1| 8|
+----+----+----+----+----+----+
| 1| 2| 5| 1| 5|null|
| 3| 4| 7| 8|null| 7|
+----+----+----+----+----+----+