Filter rows based on variables “beginning with” strings specified by vector

Question

I\'m trying to filter a patient database based on specific ICD9 (diagnosis) codes. I would like to use a vector indicating the first 3 strings of the ICD9 codes.

The exa

Answer 1

You can use apply and ldply

library(plyr)
filtered_obs <- apply(observations, 1, function(x) if(sum(substr(x,1,3) %in% dx)>0){x})
filtered_obs <- plyr::ldply(filtered_obs,rbind)

If you have variable number of characters then this should work-

filtered_obs <- lapply(dx, function(y)
                 {
                  plyr::ldply(apply(observations, 1, function(x) 
                   {
                    if(sum(substr(x,1,nchar(y)) %in% y)>0){x}
                   }), rbind)
                 })

filtered_obs <- unique(plyr::ldply(filtered_obs,rbind))