Reading partitions one at a time from Python

ankitmat45

Hi, I am trying to read a partitioned dataset using Python. I got a list of partitions using the following code. But I do not know how to read those partitions one by one as dataframe.

mydataset = dataiku.Dataset("Data")
mydataset_df = mydataset.list_partitions(raise_if_empty=True)

Kindly suggest

Thanks

fchataigner2

Hi,

in a notebook, you'd go like:

import dataiku
ds = dataiku.Dataset('Data')
for p in ds.list_partitions():
    ds.read_partitions = [p]
    df = ds.get_dataframe()
    print(df.shape)

Note that in a recipe, the read_partitions field will be filled by DSS automatically when you create the Dataset object.

Regards,

Frederic

Nicolas_Servel

Hello,

First, are you trying to achieve that from a python recipe (in the flow), or from a notebook ? If you are in a python recipe, you usually cannot handle yourself partitions, as they are managed in the recipe parameters. However, you can override that by setting the "ignore_flow" field to "True" in every occurence of "Dataset". It would look like

import dataiku
my_dataset = dataiku.Dataset("my_dataset_name", ignore_flow=True)

Then, the solution to read only some partitions of a dataset is to leverage the "add_read_partitions" function from the "Dataset" class. However, this functions only "adds" the partition, meaning, it does not remove the previously added ones. Therefore, each time you call it, you need to reset th read partition by using a new instance of Dataset. This would look like:

import dataiku
partitions = dataiku.Dataset("Data").list_partitions(raise_if_empty=True)
dataset_partitions_df = {}
for partition in partitions:
    dataset = dataiku.Dataset("Data")  # reinitializing the read partition
    dataset.add_read_partitions(partition)
    dataset_partition_df = dataset.get_dataframe()
    dataset_partitions_df[partition] = dataset_partition_df
print(dataset_partitions_df)
# => outputs {"part1": .. df of part1 .., "part2": .. df of part2 .., ...}

Hope this helps

Best regards

Skanda Gurunathan

Why is the list_partitions() taking a lot of time, how does internally dataiku works on this?

Say I want to read only the latest partition, is there anyway to get that quickly?