R filtering out a subset

Question

I have a data.frame A and a data.frame B which contains a subset of A

How can I create a data.frame C which is data.frame A with data.frame B excluded? Thanks for your h

Answer 1

Here are two data.table solutions that will be memory and time efficient

render_markdown(strict = T)
library(data.table)
# some biggish data
set.seed(1234)
ADT <- data.table(x = seq.int(1e+07), y = seq.int(1e+07))

.rows <- sample(nrow(ADT), 30000)
# Random subset of A in B
BDT <- ADT[.rows, ]

# set keys for fast merge
setkey(ADT, x)
setkey(BDT, x)
## how CDT <- ADT[-ADT[BDT,which=T]] the data as `data.frames for fastest
## alternative
A <- copy(ADT)
setattr(A, "class", "data.frame")
B <- copy(BDT)
setattr(B, "class", "data.frame")
f2 <- function() noBDT <- ADT[-ADT[BDT, which = T]]
f3 <- function() noBDT2 <- ADT[-BDT[, x]]
f1 <- function() noB <- A[-as.integer(rownames(B)), ]

library(rbenchmark)
benchmark(base = f1(),DT = f2(), DT2 = f3(), replications = 3)

##   test replications elapsed relative user.self sys.self 
## 2   DT            3    0.92    1.108      0.77     0.15       
## 1  base           3    3.72    4.482      3.19     0.52        
## 3  DT2            3    0.83    1.000      0.72     0.11