Pyspark dataframe left join with default values

Question

I have two dataframes df1 and df2. I am trying to join (left join)

df1:

Name     ID       Age
AA       1        23
BB       2        49
CC       3        76
DD       4        27
EE       5        43
FF       6        34
GG       7        65

df2:

ID      Place
1       Germany
3       Holland
7       India

Final = df1.join(df2, on=['ID'], how='left')

    Name     ID       Age    Place
    AA       1        23     Germany
    BB       2        49     null
    CC       3        76     Holland
    DD       4        27     null
    EE       5        43     null
    FF       6        34     null
    GG       7        65     India

But I would like to fill the Place column with Name column value if place value is null

Expected output:

    Name     ID       Age    Place
    AA       1        23     Germany
    BB       2        49     BB
    CC       3        76     Holland
    DD       4        27     DD
    EE       5        43     EE
    FF       6        34     FF
    GG       7        65     India

Solution, I can think of is, once the join is completed, I can check the value of Place and replace with Name if it's null. Please let me know if there are any other elegant way of solution. Thanks.

try this: final = df1.merge(df2,on='ID',how='left').assign(Place=lambda x: x['Place'].fillna(x['Name'])) — anky
– anky, Commented Jan 30, 2020 at 3:34
Sorry, I forgot to mention that I am trying to do this in pyspark dataframe. merge and assign does not work with pyspark dataframe. Thanks. — Lilly
– Lilly, Commented Jan 30, 2020 at 5:21

Lilly · Accepted Answer · 2020-01-30 07:30:37Z

3

Yes, Thanks. After some search managed to use as shown in the link below

from pyspark.sql.functions import coalesce
df1.withColumn("Place",coalesce(df1.Place,df.Name))

Another thread

answered Jan 30, 2020 at 7:30

Lilly

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