Suppose there is a dateframe with a column comprised of dates as strings. For that assumption, we create the following dataFrame as an example:
# Importing sql types
from pyspark.sql.types import StringType, IntegerType, StructType, StructField, DoubleType, FloatType, DateType
from pyspark.sql.functions import date_format
import random
import time
def strTimeProp(start, end, format, prop):
stime = time.mktime(time.strptime(start, format)) # Parse a string representing a time according to a format
etime = time.mktime(time.strptime(end, format))
ptime = stime + prop * (etime - stime)
return time.strftime(format, time.localtime(ptime))
def randomDate(start, end, prop):
return strTimeProp(start, end, '%m-%d-%Y', prop)
# Creación de un dataframe de prueba:
schema = StructType(
[
StructField("dates1", StringType(), True),
StructField("dates2", StringType(), True)
]
)
size = 32
numCol1 = [str(randomDate("1-1-1991", "1-1-1992", random.random())) for number in range(size)]
numCol2 = [str(randomDate("1-1-1991", "1-1-1992", random.random())) for number in range(size)]
# Building dataFrame:
sqlContext = SQLContext(sc)
df = sqlContext.createDataFrame(list(zip(numCol1, numCol2)),schema=schema)
df.show(5)
In the code above, a random date column is generated, here is an example:
+----------+----------+
| dates1| dates2|
+----------+----------+
|12-21-1991|05-30-1991|
|05-28-1991|01-23-1991|
|03-01-1991|08-05-1991|
|07-15-1991|05-13-1991|
|07-21-1991|11-10-1991|
+----------+----------+
What I am trying to do is to change date format with the following code (from pySpark documentation):
# Changing date formats:
df.select(date_format('dates1', 'MM-dd-yyy').alias('newFormat')).show(5)
But I get this bad result:
+---------+
|newFormat|
+---------+
| null|
| null|
| null|
| null|
| null|
+---------+
I suppose there is a problem relate with the string dataType but at same time, I don't understand why this code bellow works and the code above don't.
fechas = ['1000-01-01', '1000-01-15']
df = sqlContext.createDataFrame(list(zip(fechas, fechas)), ['dates', 'd'])
df.show()
# Changing date formats:
df.select(date_format('dates', 'MM-dd-yyy').alias('newFormat')).show()
Output:
+----------+----------+
| dates| d|
+----------+----------+
|1000-01-01|1000-01-01|
|1000-01-15|1000-01-15|
+----------+----------+
+----------+
| newFormat|
+----------+
|01-01-1000|
|01-15-1000|
+----------+
This last results is what I want.