如何基于涉及字段的条件提取数据帧的子集？ [英] how to extract a subset of a data frame based on a condition involving a field?

问题描述

我有一个大型CSV，其中包含来自不同地点的医疗调查结果（该位置是数据中存在的因素）。由于一些分析是特定于一个位置，为了方便，我想提取子帧，只有从这些位置的行。它发生的位置是第一个字段，所以是的，我可以通过排序CSV行，但我想学习如何做到R，因为我确定我需要这个为其他列。

因此，简而言之，问题是：给定一个数据框foo，如何创建另一个数据框，其中只包含foo的行foo $ location ='there'？

非常感谢。

解决方案

是两种主要方法。我更喜欢这个可读性：

  bar < -  subset（foo，location ==there）$ b $请注意，您可以使用& 将许多条件字符串连接在一起。  | 来创建复杂的子集。
 
 
 
第二种是索引方法。您可以使用数字或布尔切片来索引R中的行。  foo $ location ==there返回向量 T 和 F 值的长度与 foo 的行长度相同。您可以这样做，只返回条件返回true的行。
  foo [foo $ location ==there 
  
 
I have a large CSV with the results of a medical survey from different locations (the location is a factor present in the data). As some analyses are specific to a location and for convenience, I'd like to extract subframes with the rows only from those locations. It happens that the location is the very first field so yes, I could do it by sorting the CSV rows, but I'd like to learn how to do it in R as I'm sure I'll need this for other columns.

So, in a nutshell, the question is: given a data frame foo, how can I create another data frame bar which only contains the rows from foo where foo$location = 'there'?

Thanks a lot.
解决方案
Here are the two main approaches. I prefer this one for its readability:
bar <- subset(foo, location == "there")
Note that you can string together many conditionals with & and | to create complex subsets.

The second is the indexing approach. You can index rows in R with either numeric, or boolean slices. foo$location == "there" returns a vector of T and F values that is the same length as the rows of foo. You can do this to return only rows where the condition returns true.
foo[foo$location == "there", ]


                        
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