R setdiff() by regex - regex

Question

Is it possible to customize setdiff using regular expressions to see what is in one vector and not another? For example:
x <- c("1\t119\t120\t1\t119\t120\tABC\tDEF\t0", "2\t558\t559\t2\t558\t559\tGHI\tJKL\t0", "3\t139\t141\t3\t139\t141\tMNO\tPQR\t0", "3\t139\t143\t3\t139\t143\tSTU\tVWX\t0")
[1] "1\t119\t120\t1\t119\t120\tABC\tDEF\t0"
[2] "2\t558\t559\t2\t558\t559\tGHI\tJKL\t0"
[3] "3\t139\t141\t3\t139\t141\tMNO\tPQR\t0"
[4] "3\t139\t143\t3\t139\t143\tSTU\tVWX\t0"
y <- c("1\t119\t120\t1\t109\t120\tABC\tDEF\t0", "2\t558\t559\t2\t548\t559\tGHI\tJKL\t0", "3\t139\t141\t3\t129\t141\tMNO\tPQR\t0", "3\t139\t143\t3\t129\t143\tSTU\tVWX\t0", "4\t157\t158\t4\t147\t158\tXWX\tYTY\t0", "5\t158\t159\t5\t148\t159\tPHP\tWZW\t0")
[1] "1\t119\t120\t1\t109\t120\tABC\tDEF\t0"
[2] "2\t558\t559\t2\t548\t559\tGHI\tJKL\t0"
[3] "3\t139\t141\t3\t129\t141\tMNO\tPQR\t0"
[4] "3\t139\t143\t3\t129\t143\tSTU\tVWX\t0"
[5] "4\t157\t158\t4\t147\t158\tXWX\tYTY\t0"
[6] "5\t158\t159\t5\t148\t159\tPHP\tWZW\t0"
I want to be able to show that:
[5] "4\t157\t158\t4\t147\t158\tXWX\tYTY\t0"
[6] "5\t158\t159\t5\t148\t159\tPHP\tWZW\t0"
are new because 4\t157\t158 and 4\t157\t158 are unique to y. This doesn't work:
> setdiff(y,x)
[1] "1\t119\t120\t1\t109\t120\tABC\tDEF\t0" "2\t558\t559\t2\t548\t559\tGHI\tJKL\t0"
[3] "3\t139\t141\t3\t129\t141\tMNO\tPQR\t0" "3\t139\t143\t3\t129\t143\tSTU\tVWX\t0"
[5] "4\t157\t158\t4\t147\t158\tXWX\tYTY\t0" "5\t158\t159\t5\t148\t159\tPHP\tWZW\t0"
Because column 5 is clearly different in both x and y. I want to setdiff only based on the first three columns.
A simple example of setdiff can be found here: How to tell what is in one vector and not another?

Answer 1

One way to do this is to put x and y as data.frames and anti-join. I'll use data.table since I find it more natural.
library(data.table)
xDT <- as.data.table(do.call("rbind", strsplit(x, split = "\t")))
yDT <- as.data.table(do.call("rbind", strsplit(y, split = "\t")))
Now anti-join (a "setdiff" for data.frames/data.tables):
yDT[!xDT, on = paste0("V", 1:3)]
# V1 V2 V3 V4 V5 V6 V7 V8 V9
# 1: 4 157 158 4 147 158 XWX YTY 0
# 2: 5 158 159 5 148 159 PHP WZW 0
You could also get the row index (thanks to #Frank for the suggested improvement/simplification):
> yDT[!xDT, which = TRUE, on = paste0("V", 1:3)]
Or extract it directly from y:
> y[yDT[!xDT, which = TRUE, on = paste0("V", 1:3)]]
# [1] "4\t157\t158\t4\t147\t158\tXWX\tYTY\t0" "5\t158\t159\t5\t148\t159\tPHP\tWZW\t0"

Answer 2

We could also use anti_join from dplyr after reading it with either fread
library(data.table)
library(dplyr)
anti_join(fread(paste(y, collapse='\n')),
fread(paste(x, collapse='\n')), by = c('V1', 'V2', 'V3'))
# V1 V2 V3 V4 V5 V6 V7 V8 V9
# (int) (int) (int) (int) (int) (int) (chr) (chr) (int)
# 1 4 157 158 4 147 158 XWX YTY 0
# 2 5 158 159 5 148 159 PHP WZW 0
Or (as the title requests for regex) we can use regex to remove part of the string and then do the %in%
y[!sub('(([^\t]+\t){3}).*', '\\1', y) %in%
sub('(([^\t]+\t){3}).*', '\\1', x)]
#[1] "4\t157\t158\t4\t147\t158\tXWX\tYTY\t0" "5\t158\t159\t5\t148\t159\tPHP\tWZW\t0"