combinations - how to omit reciprocal of words in a data.frame using r -

i have been searching answer online cannot seem to anywhere close..

i have set of tickers , used expand.grid() find combinations of them:

# tickers <- c("air", "afap", "aal", "cece", "asa", "avx") # find combinations b <- expand.grid(a,a,stringsasfactors=false) 

so want omit reciprocals, example:

row 2 , row 7 reciprocals, , want keep 1 of combinations not both.

head(b,10)    var1 var2 1   air  air 2  afap  air 3   aal  air 4  cece  air 5   asa  air 6   avx  air 7   air afap 8  afap afap 9   aal afap 10 cece afap 

using initial output op, can sort 'b' row using apply margin=1, non-duplicated logical index of 'd1' rows duplicated, , use subset 'b'

d1 <- as.data.frame(t(apply(b, 1, sort))) b1 <- b[!duplicated(d1),] head(b1, 10) #   var1 var2 #1   air  air #2  afap  air #3   aal  air #4  cece  air #5   asa  air #6   avx  air #8  afap afap #9   aal afap #10 cece afap #11  asa afap 

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another compact option using data.table

library(data.table) cj(a, a)[v1>=v2]