r - How do I compare two columns and delete the not overlapping elements? -

i have 2 columns in 2 data frames, longer 1 includes elements of other column. want delete elements in longer column not overlap other, corresponding row. identified "difference" using:

diff <- setdiff(gdp$country, tfpg$country)

and tried use 2 loops done:

for (i in 1:28) { for(j in 1:123) {if(diff[i] == gdp$country[j]) {gdp <- gdp[-c(j),]}}} 

where 28 number of rows want delete (length of diff) , 123 length of longer column. not work, error message:

error in if (diff[i] == gdp$country[j]) { :    missing value true/false needed 

so how fix this? or there better way this?

thank much.

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i have data frame called "gdp" here:

  country  wto   y1990   y1991   y1992  austria 1995  251540  260197  265644  belgium 1995  322113  328017  333038  cyprus 1995   14436   14537   15898  denmark 1995  177089  179392  182936  finland 1995  149584  140737  136058  france 1995 1804032 1822778 1851937 

there 123 rows. delete rows country names specified in vector:

diff ["austria","china",...,"yemen"] 

there better way! you're describing equivalent of left join, or inner join. in r way achieve using merge command:

## s3 method class 'data.frame' merge(x, y, = intersect(names(x), names(y)),   by.x = by, by.y = by, = false, all.x = all, all.y = all,   sort = true, suffixes = c(".x",".y"),   incomparables = null, ...) 

in case:

merge(gdp, tfpg, = intersect('country', 'country')) 

e.g.

x = data.frame(foo = c(1,2,3,4,5), bar=c("a","b","c","d","e")) y = data.frame(baz = c(6,7,8,9), bar=c("a","c","e","f")) z = merge(x,y,by=intersect('bar','bar')) 

gives

  bar foo baz 1     1   6 2   c   3   7 3   e   5   8