根据涉及字段的条件提取数据框的子集 [英] Extract a subset of a dataframe based on a condition involving a field

问题描述

我有一个很大的CSV文件，其中包含来自不同位置的医学调查结果(该位置是数据中存在的一个因素).由于某些分析特定​​于某个位置并且为了方便起见，我只想从那些位置中提取带有行的子帧.碰巧位置是第一个字段，所以是的，我可以通过对CSV行进行排序来实现，但是我想学习如何在R中执行此操作，因为我确定其他列也需要使用它.

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.

因此，总而言之，问题是:给定一个数据框foo，我如何创建另一个仅包含foo中foo$location = 'there'行的行的数据框栏?

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'?

推荐答案

以下是两种主要方法.我更喜欢它的可读性:

Here are the two main approaches. I prefer this one for its readability:

bar <- subset(foo, location == "there")

请注意，您可以使用&和|将许多条件字符串组合在一起以创建复杂的子集.

Note that you can string together many conditionals with & and | to create complex subsets.

第二个是索引方法.您可以使用数字或布尔切片来索引R中的行. foo$location == "there"返回T和F值的向量，该向量的长度与foo的行相同.您可以执行此操作以仅返回条件返回true的行.

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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