Question

I tried this but this will again required a for-loop to compare so any better method to find the index.

str[[1]][1]  
"NYA.FWD.AMGM.MON..MAXRUNALARM."
m<-grep( str[[1]][1] , colnames(log_data)[2:ncol(log_data)] , value=FALSE)
m
[1] 5 6

where

colnames(log_data)[6]
"NYA.FWD.AMGM.MON..MAXRUNALARM....SU."
colnames(log_data)[7]
"NYA.FWD.AMGM.MON..MAXRUNALARM."

I only want the 6 as indices ,means the exact length of the string or is there an better method to extract the similar string of same length.

I also used

str_detect((colnames(log_data)[2:ncol(log_data)]),fixed(str[[1]][1]))
[1] FALSE FALSE FALSE FALSE  **TRUE  TRUE** FALSE FALSE FALSE FALSE FALSE FALSE
[13] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE

but getting the logical vectors just want a single index ,thank you.

Answer 1

If you want an exact match, use match:

match(str[[1]][1], colnames(log_data)[2:ncol(log_data)])

It will return the index of the first match. If you have multiple matches and want all their indices, do:

which(str[[1]][1] == colnames(log_data)[2:ncol(log_data)])