Get the same rows from two data frames without merge or dplyr

Question

I have to get the same rows from two datasets without using function as merge or packages like dplyr. basically I can only use for cycles and if.

I've come up to this solution:

#since the two data frames are really big, I've reduced them using:

tab1 <- tab1[seq(800,1000),]
tab2 <- tab2[seq(800,1000),]

rname1 <- rownames(tab1)
rname2 <- rownames(tab2)
vecres <- c()

#since I need the results from only the first 3 columns of datasets:

for (i in rname1) { 
  a <- tab1[i,c(1,2,3)]
  for (j in rname2) {
    b <- tab2[j,c(1,2,3)] 
   
    cond <- a == b
    singlecond <- all(cond)
   
    if (singlecond) {vecres[i] <- c(a[i,c(1,2,3)])} 
      
    
  }
  
}

I. don't know how to go on and where I'm making mistakes... please help!

Answer 1

You can try the code below

tab1[do.call(paste, tab1[1:3]) %in% do.call(paste, tab2[1:3]), ]

If you really want for loops, you can try

vecres <- c()
for (i in rname1) {
    a <- tab1[i, c(1, 2, 3)]
    for (j in rname2) {
        b <- tab2[j, c(1, 2, 3)]

        cond <- a == b
        singlecond <- all(cond)

        if (singlecond) {
            vecres <- c(vecres, i)
        }
    }
}
tab1[vecres,]