问基于单个代码的上游河段识别

EN

a <- c(41397427, 41397438, 41397439, 41397440, 41397466, 41397467, 41397494, 41397495, 41397512, 41397513, 41397514, 41397566, 41397584)
b <- c(41397438, 41397494, 41397466, 41397439, 41397438, 41397440, 41397401, 41397440, 41397466, 41397439, 41397495, 41397495, 41397494)

# Data frame of individual codes for reach id (HYRIV_ID) and the next downstream reach (NEXT_DOWN)
df <- data.frame(HYRIV_ID = a, NEXT_DOWN = b)

# Point A and B HYRIV_ID
id <- c(41397494, 41397495)

# NOTE: Although the loop will run, the output of i = 1 (point A) is not correct, as it's only identifying the first upstream reaches 

pt_up <- list() # create a list to store the upstream HYRIV_ID for each target code in id
for (i in 1:length(id)){
  n <- id[[i]] # creates vector with target HYRIV_ID, where all upstream reaches will also be stored
  tmp_id <- df[df$NEXT_DOWN == id[[i]],]$HYRIV_ID # identifies reaches which have n as NEXT_DOWN reach

  # if the target reach is the most upstream, then it can't be downstream of any other
  if(length(tmp_id) == 0){
    n <- n
    # if not, I need to find the next upstream reaches
    }else{
      # If tmp_id is higher than 1 I need to find the upstream reaches of each HYRIV_ID in tmp_id
      # I use a second loop go through codes stored in tmp_id 
     for (j in 1:length(tmp_id)){
       tmp_id2 <- df[df$NEXT_DOWN == tmp_id[[j]],]$HYRIV_ID
       if(length(tmp_id2) == 0){
         n <- append(n, tmp_id[[j]]) # if tmp_id2 as no upstream reaches, then I add the codes in tmp_id to n, as this will be the only upstream reaches
       }else{
         n <- append(n, tmp_id2) 
       }
     }
    }
  pt_up[[i]] <- n # add reaches HYRIV_ID upstream of target reach to the list 
  names(pt_up)[i] <- id[[i]] # name list element to keep track of target reach
  
  }

pt_up <- list() # create a list to store the upstream HYRIV_ID for each target code in id
for (i in 1:length(id)){
  n <- id[[i]] # creates vector with target HYRIV_ID, where all upstream reaches will also be stored
  tmp_id <- df[df$NEXT_DOWN == id[[i]],]$HYRIV_ID # identifies reaches which have n as NEXT_DOWN reach
  
  # if the target reach is the most upstream, then it can't be downstream of any other
  if(length(tmp_id) == 0){
    n <- n
    # if not, I need to find the next upstream reaches
  }else{
    # If tmp_id is higher than 1 I need to find the upstream reaches of each HYRIV_ID in tmp_id
    # I use a second loop go through codes stored in tmp_id 
    n <- append(n, tmp_id) # adds the HYRIV_ID of the first upstream reaches
    tmp_id2 <- tmp_id # create a new vector that will be updated within the loop, without overwriting
    
    ####### NEW SECTION ADDED HERE ######
    repeat{ # this is where I added the repeat loop    
      for (j in 1:length(tmp_id2)){ # loops through all HYRIV_IDs stored in tmp_2 and repeats after tmp_id2 is updated
      if(length(df[df$NEXT_DOWN == tmp_id2[[j]],]$HYRIV_ID) == 0){
        n <- n # if tmp_id2 has no upstream reaches, then I add the codes in tmp_id to n, as this will be the only upstream reaches
      }else{
        id2 <- df[df$NEXT_DOWN == tmp_id2[[j]],]$HYRIV_ID # HYRIV_ID upstream of codes stored in tmp_id2
        n <- append(n, id2) # add codes to n
      }
      }
      tmp_id2 <- id2 # updated tmp_id2 with the new IDs so to repeat the loop
      if (length(df[df$NEXT_DOWN %in% tmp_id2,]$HYRIV_ID) == 0 & unique(tmp_id2 %in% n) == TRUE){
        break 
      } # this will stop the repeat loop when there are no upstream reaches left 
    }
    ####### END OF NEW SECTION ######

  pt_up[[i]] <- n # add reaches HYRIV_ID upstream of target reach to the list 
  names(pt_up)[i] <- id[[i]] # name list element to keep track of target reach
  }
}