Multi tool use

How to flat map a dataframe with unequal lists?

I have a data frame as follows-

a | b | c
[1] | [3,4,5,6] | [7,8,9,10]


i need the output as

a | b | c
1 3 7
1 4 8
1 5 9
1 6 10


Currently i am getting output as below upon using the following statement-

cols=['a','b','c']
df.rdd.flatMap(lambda x: itertools.izip_longest(*[x[c] for c in cols])).toDF(cols)

a | b | c
1 3 7
null 4 8
null 5 9
null 6 10


The number of columns are not fixed. If the solution is a generalized it would be helpful.

1 Answer
1

One option is to use itertools.repeat to repeat each array whose length is less than length of the longest array.

itertools.repeat

from itertools import izip_longest, repeat, chain

cols = df.columns
def zip_with_repeat(row, cols):
M = max(len(row[c]) for c in cols)
return izip_longest(
*[list(chain(*repeat(row[c], (M - len(row[c])) + 1)))[:M] for c in cols]
)

df.rdd.flatMap(lambda row: zip_with_repeat(row, cols)).toDF(cols).show()
#+---+---+---+
#| a| b| c|
#+---+---+---+
#| 1| 3| 7|
#| 1| 4| 8|
#| 1| 5| 9|
#| 1| 6| 10|
#+---+---+---+


For illustrative purposes, suppose you instead had the following DataFrame:

#+--------+------------+-------------+
#| a| b| c|
#+--------+------------+-------------+
#| [1]|[3, 4, 5, 6]|[7, 8, 9, 10]|
#|[10, 20]|[30, 40, 50]| [70, 80, 90]|
#+--------+------------+-------------+


The code would produce:

#+---+---+---+
#| a| b| c|
#+---+---+---+
#| 1| 3| 7|
#| 1| 4| 8|
#| 1| 5| 9|
#| 1| 6| 10|
#| 10| 30| 70|
#| 20| 40| 80|
#| 10| 50| 90|
#+---+---+---+


Notice that the 10 repeated once to fill in the array in column a to the appropriate length.

10

a

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