使用Ruby CSV提取一列 [英] Using Ruby CSV to extract one column

问题描述

我一直在尝试从csv文件中获取单列.

I've been trying to work with getting a single column out of a csv file.

我已经阅读了文档， http://www.ruby-doc.org/stdlib/libdoc/csv/rdoc/index.html 但仍然不太了解如何使用它.

I've gone through the documentation, http://www.ruby-doc.org/stdlib/libdoc/csv/rdoc/index.html but still don't really understand how to use it.

如果使用CSV.table，与CSV.read相比，响应速度非常慢.我承认我要加载的数据集非常大，这正是我只想从中获取单个列的原因.

If I use CSV.table, the response is incredibly slow compared to CSV.read. I admit the dataset I'm loading is quite large, which is exactly the reason I only want to get a single column from it.

我的请求目前看起来像这样

My request is simply currently looks like this

@dataTable = CSV.table('path_to_csv.csv')

当我调试时，我得到一个响应

and when I debug I get a response of

#<CSV::Table mode:col_or_row row_count:2104 >

文档说我应该能够使用

The documentation says I should be able to use by_col(), but when I try to output

<%= debug @dataTable.by_col('col_name or index') %>

它给我未定义的方法'col'错误"

It gives me "undefined method 'col' error"

有人可以向我解释如何使用CSV吗?以及是否有一种方法可以使用读取"而不是表"更快地获取列?

Can somebody explain to me how I'm supposed to use CSV? and if there is a way to get columns faster using 'read' instead of 'table'?

我使用的是Ruby 1.92，它表示它使用的是fastCSV，因此不需要使用FasterCSV gem.

I'm using Ruby 1.92, which says that it is using fasterCSV, so I don't need to use the FasterCSV gem.

推荐答案

要从csv中抽出一列，我可能会执行以下操作:

To pluck a column out of a csv I'd probably do something like the following:

col_data = []
CSV.foreach(FILENAME) {|row| col_data << row[COL_INDEX]}

这应该比CSV上的任何操作都要快.

That should be substantially faster than any operations on CSV.Table

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