R: Read dynamic variable names generated in for loop

Question

I am generating dynamic variables names like P_1_Onsets_PRH, p_2_Onsets_PRH, etc. in a for loop. In this same loop, I'd like to read these variable names and generate corresponding matrices P1_Durations_PRH, etc. having the same number of elements as the respective Onset matrix.

for (i in 1:nrow(LabviewFiles)){
  assign(x = paste("P",i , "Onsets_PRH", sep = "_"), value = t(subset.data.frame(All_Phase, All_Phase$Phase==i) %>% 
                                                           filter(CONDITIONS == "NULL_TRIAL",
                                                                  MISC_REWARD == 1,
                                                                  MISC_PASSIVE_FAILED == 1) %>% 
                                                           select(Feedback_onset)))
  assign(x = paste("P",i , "Durations_PRH", sep = "_"), value = t(rep(0.5, times = length(noquote(paste("P",i , "Onsets_PRH", sep = "_"))))))
}

How do I read the length of matrix 'P_i_Onsets_PRH'?

I'm a newbie to R. Any help is appreciated.

Answer 1

You may use get to do this -

library(dplyr)

for (i in 1:nrow(LabviewFiles)){
  assign(x = paste("P",i , "Onsets_PRH", sep = "_"), value = t(subset.data.frame(All_Phase, All_Phase$Phase==i) %>% 
                                                                 filter(CONDITIONS == "NULL_TRIAL",
                                                                        MISC_REWARD == 1,
                                                                        MISC_PASSIVE_FAILED == 1) %>% 
                                                                 select(Feedback_onset)))

  assign(x = paste("P",i , "Durations_PRH", sep = "_"), value = t(rep(0.5, times = length(get(paste("P",i , "Onsets_PRH", sep = "_"))))))
}

Note that using assign and creating variables in global environment is discouraged. You may also read Why is using assign bad?