pandas.read_csv中的usecols函数实现读取指定列

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pandas.read_csv的usecols参数允许用户指定读取数据框的特定列。它可以接受列表形式的列索引或名称，或者一个可调用函数，根据返回值筛选列。例如，usecols=[0, 1, 2, 3]将读取前四列，此参数能提高解析速度并降低内存消耗。" 126919496,10181518,Tomcat集群session共享策略详解,"['tomcat', 'java', 'servlet', '集群', 'session管理']

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官方解释如下：

usecols : list-like or callable, default None

Return a subset of the columns. If list-like, all elements must either be positional (i.e. integer indices into the document columns) or strings that correspond to column names provided either by the user in names or inferred from the document header row(s). For example, a valid list-like usecols parameter would be [0, 1, 2] or [‘foo’, ‘bar’, ‘baz’]. Element order is ignored, so usecols=[0, 1] is the same as [1, 0]. To instantiate a DataFrame from data with element order preserved use pd.read_csv(data,usecols=['foo', 'bar'])[['foo', 'bar']] for columns in ['foo', 'bar'] order orpd.read_csv(data, usecols=['foo', 'bar'])[['bar', 'foo']] for ['bar', 'foo'] order.

If callable, the callable function will be evaluated against the column names, returning names where the callable function evaluates to True. An example of a valid callable argument would be lambda x: x.upper() in ['AAA', 'BBB', 'DDD']. Using this parameter results in much faster parsing time and lower memory usage.’

常用的用法为：pandas.read_csv('file_name.csv', usecols = [0,1,2,3]) 读取0,1,2,3也就是前四列，中间的数可以任意指定