Given a data frame "foo", how can I select only those rows from "foo" where e.g. foo$location = "there"?
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
Desired result, "bar":
# location x y
# 2 there 2 7
# 4 there 4 9
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)], ]
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