根据列中的条件设置数据框架中的子集/筛选器行

给定一个数据帧“ foo”，如何只从“ foo”中(例如 foo$location = "there")选择那些行？

foo = data.frame(location = c("here", "there", "here", "there", "where"), x = 1:5, y = 6:10)
foo
#   location x  y
# 1     here 1  6
# 2    there 2  7
# 3     here 3  8
# 4    there 4  9
# 5    where 5 10

期望结果“吧”:

#   location x y
# 2    there 2 7
# 4    there 4 9
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最佳答案

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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Just to extend the answer above you can also index your columns rather than specifying the column names which can also be useful depending on what you're doing. Given that your location is the first field it would look like this:

    bar <- foo[foo[ ,1] == "there", ]

This is useful because you can perform operations on your column value, like looping over specific columns (and you can do the same by indexing row numbers too).

This is also useful if you need to perform some operation on more than one column because you can then specify a range of columns:

    foo[foo[ ,c(1:N)], ]

Or specific columns, as you would expect.

    foo[foo[ ,c(1,5,9)], ]
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Another option could be using the function filter from dplyr. Here is a reproducible example:

foo = data.frame(location = c("here", "there", "here", "there", "where"), x = 1:5, y = 6:10)
library(dplyr)
filter(foo, location == "there")
#>   location x y
#> 1    there 2 7
#> 2    there 4 9

Created on 2022-09-11 with reprex v2.0.2


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