I'm trying to filter a PySpark dataframe that has None
as a row value:
df.select('dt_mvmt').distinct().collect()
[Row(dt_mvmt=u'2016-03-27'),
Row(dt_mvmt=u'2016-03-28'),
Row(dt_mvmt=u'2016-03-29'),
Row(dt_mvmt=None),
Row(dt_mvmt=u'2016-03-30'),
Row(dt_mvmt=u'2016-03-31')]
and I can filter correctly with an string value:
df[df.dt_mvmt == '2016-03-31']
# some results here
but this fails:
df[df.dt_mvmt == None].count()
0
df[df.dt_mvmt != None].count()
0
But there are definitely values on each category. What's going on?
You can use Column.isNull
/ Column.isNotNull
:
df.where(col("dt_mvmt").isNull())
df.where(col("dt_mvmt").isNotNull())
If you want to simply drop NULL
values you can use na.drop
with subset
argument:
df.na.drop(subset=["dt_mvmt"])
Equality based comparisons with NULL
won't work because in SQL NULL
is undefined so any attempt to compare it with another value returns NULL
:
sqlContext.sql("SELECT NULL = NULL").show()
## +-------------+
## |(NULL = NULL)|
## +-------------+
## | null|
## +-------------+
sqlContext.sql("SELECT NULL != NULL").show()
## +-------------------+
## |(NOT (NULL = NULL))|
## +-------------------+
## | null|
## +-------------------+
The only valid method to compare value with NULL
is IS
/ IS NOT
which are equivalent to the isNull
/ isNotNull
method calls.
To obtain entries whose values in the dt_mvmt
column are not null we have
df.filter("dt_mvmt is not NULL")
and for entries which are null we have
df.filter("dt_mvmt is NULL")
There are multiple ways you can remove/filter the null values from a column in DataFrame.
Lets create a simple DataFrame with below code:
date = ['2016-03-27','2016-03-28','2016-03-29', None, '2016-03-30','2016-03-31']
df = spark.createDataFrame(date, StringType())
Now you can try one of the below approach to filter out the null values.
# Approach - 1
df.filter("value is not null").show()
# Approach - 2
df.filter(col("value").isNotNull()).show()
# Approach - 3
df.filter(df["value"].isNotNull()).show()
# Approach - 4
df.filter(df.value.isNotNull()).show()
# Approach - 5
df.na.drop(subset=["value"]).show()
# Approach - 6
df.dropna(subset=["value"]).show()
# Note: You can also use where function instead of a filter.
You can also check the section "Working with NULL Values" on my blog for more information.
I hope it helps.
isNull()
/isNotNull()
will return the respective rows which have dt_mvmt
as Null or !Null.
method_1 = df.filter(df['dt_mvmt'].isNotNull()).count()
method_2 = df.filter(df.dt_mvmt.isNotNull()).count()
Both will return the same result
if column = None
COLUMN_OLD_VALUE
----------------
None
1
None
100
20
------------------
Use create a temptable on data frame:
sqlContext.sql("select * from tempTable where column_old_value='None' ").show()
So use : column_old_value='None'
If you want to keep with the Pandas syntex this worked for me.
df = df[df.dt_mvmt.isNotNull()]
None/Null is a data type of the class NoneType in PySpark/Python so, below will not work as you are trying to compare NoneType object with the string object
Wrong way of filreting
df[df.dt_mvmt == None].count()
0
df[df.dt_mvmt != None].count()
0
correct
df=df.where(col("dt_mvmt").isNotNull())
returns all records with dt_mvmt
as None/Null
PySpark provides various filtering options based on arithmetic, logical and other conditions. Presence of NULL values can hamper further processes. Removing them or statistically imputing them could be a choice.
Below set of code can be considered:
# Dataset is df
# Column name is dt_mvmt
# Before filtering make sure you have the right count of the dataset
df.count() # Some number
# Filter here
df = df.filter(df.dt_mvmt.isNotNull())
# Check the count to ensure there are NULL values present (This is important when dealing with large dataset)
df.count() # Count should be reduced if NULL values are present
If you want to filter out records having None value in column then see below example:
df=spark.createDataFrame([[123,"abc"],[234,"fre"],[345,None]],["a","b"])
Now filter out null value records:
df=df.filter(df.b.isNotNull())
df.show()
If you want to remove those records from DF then see below:
df1=df.na.drop(subset=['b'])
df1.show()
Success story sharing
__eq__
with None ;) Andis
wouldn't work because it doesn't behave the same way.df.filter("dt_mvmt is not NULL")
handles both.