CODEWITHSUNDEEP
pythonpandasdataframepysparkapache-spark-sql
Dirigo
Dirigo

Reputation: 323

Converting Pandas DataFrame to Spark DataFrame

I had asked a previous question about how to Convert scipy sparse matrix to pyspark.sql.dataframe.DataFrame, and made some progress after reading the answer provided, as well as this article. I eventually came to the following code for converting a scipy.sparse.csc_matrix to a pandas dataframe:

df = pd.DataFrame(csc_mat.todense()).to_sparse(fill_value=0)
df.columns = header

I then tried converting the pandas dataframe to a spark dataframe using the suggested syntax:

spark_df = sqlContext.createDataFrame(df)

However, I get back the following error:

ValueError: cannot create an RDD from type: <type 'list'>

I do not believe it has anything to do with the sqlContext as I was able to convert another pandas dataframe of roughly the same size to a spark dataframe, no problem. Any thoughts?

Upvotes: 8

Views: 13076

Answers (2)

Dirigo
Dirigo

Reputation: 323

I am not sure if this question is still relevant to the current version of pySpark, but here is the solution I worked out a couple weeks after posting this question. The code is rather ugly and possibly inefficient, but I am posting it here due to the continued interest in this question.:

from pyspark import SparkContext
from pyspark.sql import HiveContext
from pyspark import SparkConf
from py4j.protocol import Py4JJavaError

myConf = SparkConf(loadDefaults=True)
sc = SparkContext(conf=myConf)
hc = HiveContext(sc)


def chunks(lst, k):
    """Yield k chunks of close to equal size"""
    n = len(lst) / k
    for i in range(0, len(lst), n):
        yield lst[i: i + n]


def reconstruct_rdd(lst, num_parts):
    partitions = chunks(lst, num_parts)
    for part in range(0, num_parts - 1):
        print "Partition ", part, " started..."
        partition = next(partitions)    # partition is a list of lists
        if part == 0:
            prime_rdd = sc.parallelize(partition)
        else:
            second_rdd = sc.parallelize(partition)
            prime_rdd = prime_rdd.union(second_rdd)
        print "Partition ", part, " complete!"
    return prime_rdd


def build_col_name_list(len_cols):
    name_lst = []
    for i in range(1, len_cols):
        idx = "_" + str(i)
        name_lst.append(idx)
    return name_lst


def set_spark_df_header(header, sdf):
    oldColumns = build_col_name_lst(len(sdf.columns))
    newColumns = header
    sdf = reduce(lambda sdf, idx: sdf.withColumnRenamed(oldColumns[idx], newColumns[idx]), xrange(len(oldColumns)), sdf)
    return sdf


def convert_pdf_matrix_to_sdf(pdf, sdf_header, num_of_parts):
    try:
        sdf = hc.createDataFrame(pdf)
    except ValueError:
        lst = pdf.values.tolist()   #Need to convert to list of list to parallelize
        try:
            rdd = sc.parallelize(lst)
        except Py4JJavaError:
            rdd = reconstruct_rdd(lst, num_of_parts)
            sdf = hc.createDataFrame(rdd)
            sdf = set_spark_df_header(sdf_header, sdf)
    return sdf

Upvotes: 2

user10136015
user10136015

Reputation: 1

to_sparse(fill_value=0) is basically obsolete. Just use standard variant 

sqlContext.createDataFrame(pd.DataFrame(csc_mat.todense()))

and as long as types are compatible you'd be fine.

Upvotes: 0

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