使用pyspark读取CSV文件时，命令参数与pandas略有区别，注意区分。
例如：
首行是否为列名？
分隔符如何制定？
from pyspark.sql import SparkSession
spark = SparkSession().builder.master("local").appName("read csv").getOrCreate()
df = spark.read.csv(path="/data/train.csv", header=True)下面是官方的参数说明：
Help on method csv in module pyspark.sql.readwriter:
csv(path, schema=None, sep=None, encoding=None, quote=None, escape=None, comment=None, header=None, inferSchema=None, ignoreLeadingWhiteSpace=None, ignoreTrailingWhiteSpace=None, nullValue=None, nanValue=None, positiveInf=None, negativeInf=None, dateFormat=None, timestampFormat=None, maxColumns=None, maxCharsPerColumn=None, maxMalformedLogPerPartition=None, mode=None, columnNameOfCorruptRecord=None, multiLine=None, charToEscapeQuoteEscaping=None, samplingRatio=None, enforceSchema=None, emptyValue=None) method of pyspark.sql.readwriter.DataFrameReader instance
Loads a CSV file and returns the result as a :class:`DataFrame`.
This function will go through the input once to determine the input schema if
``inferSchema`` is enabled. To avoid going through the entire data once, disable
``inferSchema`` option or specify the schema explicitly using ``schema``.
:param path: string, or list of strings, for input path(s),
or RDD of Strings storing CSV rows.
:param schema: an optional :class:`pyspark.sql.types.StructType` for the input schema
or a DDL-formatted string (For example ``col0 INT, col1 DOUBLE``).
:param sep: sets a single character as a separator for each field and value.
If None is set, it uses the default value, ``,``.
:param encoding: decodes the CSV files by the given encoding type. If None is set,
it uses the default value, ``UTF-8``.
:param quote: sets a single character used for escaping quoted values where the
separator can be part of the value. If None is set, it uses the default
value, ``"``. If you would like to turn off quotations, you need to set an
empty string.
:param escape: sets a single character used for escaping quotes inside an already
quoted value. If None is set, it uses the default value, ``\``.
:param comment: sets a single character used for skipping lines beginning with this
character. By default (None), it is disabled.
:param header: uses the first line as names of columns. If None is set, it uses the
default value, ``false``.
:param inferSchema: infers the input schema automatically from data. It requires one extra
pass over the data. If None is set, it uses the default value, ``false``.
:param enforceSchema: If it is set to ``true``, the specified or inferred schema will be
forcibly applied to datasource files, and headers in CSV files will be
ignored. If the option is set to ``false``, the schema will be
validated against all headers in CSV files or the first header in RDD
if the ``header`` option is set to ``true``. Field names in the schema
and column names in CSV headers are checked by their positions
taking into account ``spark.sql.caseSensitive``. If None is set,
``true`` is used by default. Though the default value is ``true``,
it is recommended to disable the ``enforceSchema`` option
to avoid incorrect results.
:param ignoreLeadingWhiteSpace: A flag indicating whether or not leading whitespaces from
values being read should be skipped. If None is set, it
uses the default value, ``false``.
:param ignoreTrailingWhiteSpace: A flag indicating whether or not trailing whitespaces from
values being read should be skipped. If None is set, it
uses the default value, ``false``.
:param nullValue: sets the string representation of a null value. If None is set, it uses
the default value, empty string. Since 2.0.1, this ``nullValue`` param
applies to all supported types including the string type.
:param nanValue: sets the string representation of a non-number value. If None is set, it
uses the default value, ``NaN``.
:param positiveInf: sets the string representation of a positive infinity value. If None
is set, it uses the default value, ``Inf``.
:param negativeInf: sets the string representation of a negative infinity value. If None
is set, it uses the default value, ``Inf``.
:param dateFormat: sets the string that indicates a date format. Custom date formats
follow the formats at ``java.text.SimpleDateFormat``. This
applies to date type. If None is set, it uses the
default value, ``yyyy-MM-dd``.
:param timestampFormat: sets the string that indicates a timestamp format. Custom date
formats follow the formats at ``java.text.SimpleDateFormat``.
This applies to timestamp type. If None is set, it uses the
default value, ``yyyy-MM-dd'T'HH:mm:ss.SSSXXX``.
:param maxColumns: defines a hard limit of how many columns a record can have. If None is
set, it uses the default value, ``20480``.
:param maxCharsPerColumn: defines the maximum number of characters allowed for any given
value being read. If None is set, it uses the default value,
``-1`` meaning unlimited length.
:param maxMalformedLogPerPartition: this parameter is no longer used since Spark 2.2.0.
If specified, it is ignored.
:param mode: allows a mode for dealing with corrupt records during parsing. If None is
set, it uses the default value, ``PERMISSIVE``. Note that Spark tries to
parse only required columns in CSV under column pruning. Therefore, corrupt
records can be different based on required set of fields. This behavior can
be controlled by ``spark.sql.csv.parser.columnPruning.enabled``
(enabled by default).
* ``PERMISSIVE`` : when it meets a corrupted record, puts the malformed string \
into a field configured by ``columnNameOfCorruptRecord``, and sets other \
fields to ``null``. To keep corrupt records, an user can set a string type \
field named ``columnNameOfCorruptRecord`` in an user-defined schema. If a \
schema does not have the field, it drops corrupt records during parsing. \
A record with less/more tokens than schema is not a corrupted record to CSV. \
When it meets a record having fewer tokens than the length of the schema, \
sets ``null`` to extra fields. When the record has more tokens than the \
length of the schema, it drops extra tokens.
* ``DROPMALFORMED`` : ignores the whole corrupted records.
* ``FAILFAST`` : throws an exception when it meets corrupted records.
:param columnNameOfCorruptRecord: allows renaming the new field having malformed string
created by ``PERMISSIVE`` mode. This overrides
``spark.sql.columnNameOfCorruptRecord``. If None is set,
it uses the value specified in
``spark.sql.columnNameOfCorruptRecord``.
:param multiLine: parse records, which may span multiple lines. If None is
set, it uses the default value, ``false``.
:param charToEscapeQuoteEscaping: sets a single character used for escaping the escape for
the quote character. If None is set, the default value is
escape character when escape and quote characters are
different, ``\0`` otherwise.
:param samplingRatio: defines fraction of rows used for schema inferring.
If None is set, it uses the default value, ``1.0``.
:param emptyValue: sets the string representation of an empty value. If None is set, it uses
the default value, empty string.
>>> df = spark.read.csv('python/test_support/sql/ages.csv')
>>> df.dtypes
[('_c0', 'string'), ('_c1', 'string')]
>>> rdd = sc.textFile('python/test_support/sql/ages.csv')
>>> df2 = spark.read.csv(rdd)
>>> df2.dtypes
[('_c0', 'string'), ('_c1', 'string')]
.. versionadded:: 2.0现在都要用spark做分布式计算，学一些防身。
