Question

I want to multiply two data.frames that are of unequal length
If I have a data frame of observations (in reality this is around 30000 entries long)

Species    number
1          3
1          3
3          5
4          40
5          22

and another data frame with conversion ratios for each species present in the first data frame (this is only about 120 entries in length)

species    conversion ratio
1          3
2          5
3          4
4          2
5          2

and I want to multiply each number column entry by the conversion ratio entry associated with that Species, how might I go about doing this in R?

I’ve attempted using the match function to no avail, and my attempts at working with arrays have only resulted in errors, as well.

Answer 1

See ?merge. Assuming you have species named consistently (capitals):

df3 <- merge(df1,df2)
df3$number*df3$conversion.ratio