Filter data table by dynamic column name

Question

lets say I have a data.table with columns A, B and C

I\'d like to write a function that applies a filter (for example A>1) but \"A\" needs to be dynamic (the functio

Answer 1

If your data is

a <- c(1:9)
b <- c(10:18)
# create a data.frame
df <- data.frame(a,b)
# or a data.table
dt <- data.table(a,b)

you can store your condition(s) in a variable x

x <- quote(a >= 3)

and filter the data.frame using dplyr (subsetting with [] won't work)

library(dplyr)
filter(df, x)

or using data.table as suggested by @Frank

library(data.table)
dt[eval(x),]