R - Match a value from one data frame with multiple values from another

Question

For example, say I have the two data frames...

d1 <- data.frame(c(a,b,c,d,e,f))
d2 <- data.frame(c(a,a,a,b,b,d,d,d,d,d,e,e,f))

And I want to search 'a' from d1 in d2 and reveal the index of every matching value, which can be stored in a vector.

I've searched for and played around with the Match() function, but this only seems to work when there is just one matching value.

Thanks

Unless those letters are objects, they need to be quoted, and you should probably also give the variables names so they don't end up gross. Also, you're looking for the [data.frame] tag, not [dataframes]. — alistaire
– alistaire, Commented Mar 25, 2016 at 18:28

cderv · Accepted Answer · 2016-03-25 18:27:49Z

1

To match a value from one data frame with multiple values from another, you could loop through the first data.frame and get the indice in the second for each value.

d1 <- data.frame(x = c("a","b","c","d","e","f"), stringsAsFactors = F)
d2 <- data.frame(x = c("a","a","a","b","b","d","d","d","d","d","e","e","f"), stringsAsFactors = F)

sapply(d1$x, function(value) which(d2 == value))
#> $a
#> [1] 1 2 3
#> 
#> $b
#> [1] 4 5
#> 
#> $c
#> integer(0)
#> 
#> $d
#> [1]  6  7  8  9 10
#> 
#> $e
#> [1] 11 12
#> 
#> $f
#> [1] 13

answered Mar 25, 2016 at 18:27

cderv

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1 Comment

h7681 Over a year ago

which(d2 == value)) is exactly what I was looking for. Thank you.

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