[英]Google Cloud Dataflow Write to CSV from dictionary
I have a dictionary of values that I would like to write to GCS as a valid .CSV file using the Python SDK. 我有一个值字典,我想使用Python SDK将其写入GCS作为有效的.CSV文件。 I can write the dictionary out as newline separated text file, but I can't seem to find an example converting the dictionary to a valid .CSV.
我可以将字典写成换行符分隔的文本文件,但我似乎找不到将字典转换为有效.CSV的示例。 Can anybody suggest the best way to generate csv's within a dataflow pipeline?
任何人都可以建议在数据流管道中生成csv的最佳方法吗? This answers to this question address Reading from CSV files, but don't really address writing to CSV files.
这回答了这个问题的地址从CSV文件中读取,但并没有真正解决写入CSV文件的问题。 I recognize that CSV files are just text files with rules, but I'm still struggling to convert the dictionary of data to a CSV that can be written using WriteToText.
我认识到CSV文件只是带有规则的文本文件,但我仍然在努力将数据字典转换为可以使用WriteToText编写的CSV。
Here is a simple example dictionary that I would like to turn into a CSV: 这是一个简单的示例字典,我想将其转换为CSV:
test_input = [{'label': 1, 'text': 'Here is a sentence'},
{'label': 2, 'text': 'Another sentence goes here'}]
test_input | beam.io.WriteToText(path_to_gcs)
The above would result in a text file that had each dictionary on a newline. 以上将导致文本文件在换行符上包含每个字典。 Is there any functionality within Apache Beam that I can take advantage of (similar to csv.DictWriter )?
我可以利用Apache Beam中的任何功能(类似于csv.DictWriter )吗?
Generally you will want to write a function that can convert your original dict
data elements into a csv-formatted string
representation. 通常,您需要编写一个可以将原始
dict
数据元素转换为csv格式的string
表示形式的函数。
That function can be written as a DoFn
that you can apply to your Beam PCollection
of data, which would convert each collection element into the desired format; 该函数可以写为
DoFn
,您可以将其应用于您的Beam PCollection
数据,这将把每个集合元素转换为所需的格式; you can do this by applying the DoFn
to your PCollection
via ParDo
. 您可以通过应用做到这一点
DoFn
您PCollection
通过ParDo
。 You can also wrap this DoFn
in a more user-friendly PTransform
. 您还可以将此
DoFn
包装在更加用户友好的PTransform
。
You can learn more about this process in the Beam Programming Guide 您可以在Beam Programming Guide中了解有关此过程的更多信息
Here is a simple, translatable non-Beam example: 这是一个简单的,可翻译的非梁示例:
# Our example list of dictionary elements
test_input = [{'label': 1, 'text': 'Here is a sentence'},
{'label': 2, 'text': 'Another sentence goes here'}]
def convert_my_dict_to_csv_record(input_dict):
""" Turns dictionary values into a comma-separated value formatted string """
return ','.join(map(str, input_dict.values()))
# Our converted list of elements
converted_test_input = [convert_my_dict_to_csv_record(element) for element in test_input]
The converted_test_input
will look like the following: converted_test_input
将如下所示:
['Here is a sentence,1', 'Another sentence goes here,2']
Beam DictToCSV DoFn and PTransform example using DictWriter
使用
DictWriter
Beam DictToCSV DoFn和PTransform示例
from csv import DictWriter
from csv import excel
from cStringIO import StringIO
...
def _dict_to_csv(element, column_order, missing_val='', discard_extras=True, dialect=excel):
""" Additional properties for delimiters, escape chars, etc via an instance of csv.Dialect
Note: This implementation does not support unicode
"""
buf = StringIO()
writer = DictWriter(buf,
fieldnames=column_order,
restval=missing_val,
extrasaction=('ignore' if discard_extras else 'raise'),
dialect=dialect)
writer.writerow(element)
return buf.getvalue().rstrip(dialect.lineterminator)
class _DictToCSVFn(DoFn):
""" Converts a Dictionary to a CSV-formatted String
column_order: A tuple or list specifying the name of fields to be formatted as csv, in order
missing_val: The value to be written when a named field from `column_order` is not found in the input element
discard_extras: (bool) Behavior when additional fields are found in the dictionary input element
dialect: Delimiters, escape-characters, etc can be controlled by providing an instance of csv.Dialect
"""
def __init__(self, column_order, missing_val='', discard_extras=True, dialect=excel):
self._column_order = column_order
self._missing_val = missing_val
self._discard_extras = discard_extras
self._dialect = dialect
def process(self, element, *args, **kwargs):
result = _dict_to_csv(element,
column_order=self._column_order,
missing_val=self._missing_val,
discard_extras=self._discard_extras,
dialect=self._dialect)
return [result,]
class DictToCSV(PTransform):
""" Transforms a PCollection of Dictionaries to a PCollection of CSV-formatted Strings
column_order: A tuple or list specifying the name of fields to be formatted as csv, in order
missing_val: The value to be written when a named field from `column_order` is not found in an input element
discard_extras: (bool) Behavior when additional fields are found in the dictionary input element
dialect: Delimiters, escape-characters, etc can be controlled by providing an instance of csv.Dialect
"""
def __init__(self, column_order, missing_val='', discard_extras=True, dialect=excel):
self._column_order = column_order
self._missing_val = missing_val
self._discard_extras = discard_extras
self._dialect = dialect
def expand(self, pcoll):
return pcoll | ParDo(_DictToCSVFn(column_order=self._column_order,
missing_val=self._missing_val,
discard_extras=self._discard_extras,
dialect=self._dialect)
)
To use the example, you would put your test_input
into a PCollection
, and apply the DictToCSV
PTransform
to the PCollection
; 要使用该示例,您可以将
test_input
放入PCollection
,并将DictToCSV
PTransform
应用于PCollection
; you can take the resulting converted PCollection
and use it as input for WriteToText
. 您可以获取生成的转换
PCollection
并将其用作WriteToText
输入。 Note that you must provide a list or tuple of column names, via the column_order
argument, corresponding to keys for your dictionary input elements; 请注意,您必须通过
column_order
参数提供列名或列名,对应于词典输入元素的键; the resulting CSV-formatted string columns will be in the order of the column names provided. 生成的CSV格式的字符串列将按提供的列名称的顺序排列。 Also, the underlying implementation for the example does not support
unicode
. 此外,该示例的底层实现不支持
unicode
。
Based on Andrew's suggestion, here is a ConvertDictToCSV function that I created: 根据Andrew的建议,这是我创建的ConvertDictToCSV函数:
def ConvertDictToCSV(input_dict, fieldnames, separator=",", quotechar='"'):
value_list = []
for field in fieldnames:
if input_dict[field]:
field_value = str(input_dict[field])
else:
field_value = ""
if separator in field_value:
field_value = quotechar + field_value + quotechar
value_list.append(field_value)
return separator.join(value_list)
This appears to be working well, but would certainly be safer to make use of csv.DictWriter if possible 这似乎运行良好,但如果可能的话,使用csv.DictWriter肯定会更安全
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