Nested for loop giving error despite working non-nested

Question

I am having some trouble with a nested for loop. If I run the code without nesting the for loop, I get the outcome I want. I need it to happen within the nest though, but I currently get an error stating:

"Error in data.frame(..., check.names = FALSE) : arguments imply differing number of rows: 0, 1"

Although, I don't get this when I run it outside of the for-loop. Do you have any advice on how I should proceed to get running as a nested loop?

Here is sample data

Route    Year    ID   Amount
1         1       A       5
1         2       A       2
1         3       A       7
1         4       A       1
1         1       B       5
1         2       B       11
1         3       B       0
1         4       B       2

ID_list<- unique(data$ID)

for(i in 1:length(ID_list)){
ID <- data[which(data$ID== ID_list[i]), ]
route_list <- unique(ID$Route)
for(j in 1:length(route_list)){
SP_R <- ID[which(ID$Route == route_list[j]), ]
for(k in 1:(nrow(SP_R)-1)){
  for(l in (k+1):nrow(SP_R)){
    new_data<- rbind(new_data,cbind(SP_R[k,],SP_R[l,]))
  }}}}

This gives me the error. I'm guessing it is because k and l are different lengths, but if I run the last part outside of the for loop (as a separate one - see below) it works.

for(i in 1:length(ID_list)){
ID <- data[which(data$ID== ID_list[i]), ]
route_list <- unique(ID$Route)
for(j in 1:length(route_list)){
SP_R <- ID[which(ID$Route == route_list[j]), ]
}}

for(k in 1:(nrow(SP_R)-1)){
  for(l in (k+1):nrow(SP_R)){
    new_data<- rbind(new_data,cbind(SP_R[k,],SP_R[l,]))
  }}

I have no idea why this would be. Thank you for your advice!

`ID`, `all_fifty`, `SP_R` etc., what are they? Please post a [reproducible example](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example). — AkselA, Feb 08 '18 at 18:30
Sorry about that! I have added some sample data, and cleared up the data frame names. ID is just the species ID. I basically want to subset ID, then route, then combine the rows together to get a larger dataset. — A.Spence, Feb 08 '18 at 18:57

score 0 · Answer 1 · answered Feb 09 '18 at 08:47

You have to define new_data outside the for loop like this:

new_data<-NULL

After that this will be your output:

for(i in 1:length(ID_list)){
   ID <- data[which(data$ID== ID_list[i]), ]
   route_list <- unique(ID$Route)
   for(j in 1:length(route_list)){
     SP_R <- ID[which(ID$Route == route_list[j]), ]
     for(k in 1:(nrow(SP_R)-1)){
       for(l in (k+1):nrow(SP_R)){
         new_data<- rbind(new_data,cbind(SP_R[k,],SP_R[l,]))
       }}}}

new_data
       Route Year ID Amount Route Year ID Amount
    1      1    1  A      5     1    2  A      2
    2      1    1  A      5     1    3  A      7
    3      1    1  A      5     1    4  A      1
    21     1    2  A      2     1    3  A      7
    22     1    2  A      2     1    4  A      1
    31     1    3  A      7     1    4  A      1
    5      1    1  B      5     1    2  B     11
    51     1    1  B      5     1    3  B      0
    52     1    1  B      5     1    4  B      2
    6      1    2  B     11     1    3  B      0
    61     1    2  B     11     1    4  B      2
    7      1    3  B      0     1    4  B      2

Nested for loop giving error despite working non-nested

1 Answers1