How to filter a table's row based on an external list?

Question

(1) I have a large table read in R with more than a 10000 of rows and 10 columns.

(2) The 3rd column of the table contain the name of the hospitals. Some of them are

Answer 1

Use the %in% operator.

#Sample data
dat <- data.frame(patients = 1:5, treatment = letters[1:5],
  hospital = c("yyy", "yyy", "zzz", "www", "uuu"), response = rnorm(5))

#List of hospitals we want to do further analysis on
goodHosp <- c("yyy", "uuu")

You can either index directly into your data.frame object:

dat[dat$hospital %in% goodHosp ,]

or use the subset command:

subset(dat, hospital %in% goodHosp)