How to get my function with a for loop to run through all the values-CodePudding

I am having trouble with my function 'subtract_within'. The goal of the function is for it to take a value in a variable, and then sum the differences between that value and all of the rest of the values in the variable.

When I call it, it returns the value for the first element (correctly!)in the for loop, but not the rest.

Here is my code:

x<- c(1,2,3,4,5,6) #the value i want to calculate with
y<- c(1,2,3,4,5,6) #the identifier of the value
this_df<- data.frame(x,y) 
this_df$z = 0 #now theres a new variable that is 0 for now but will be filled in later

this_df %>% 
  mutate(z = subtract_within(x,y)) #this is how i will ideally call on this function 'subtract_within'

#start of my function 'subtract_within'
subtract_within<- function(x,y){ #this function takes in two variables from a dataframe
  dataframe<- data.frame(x,y)  # i locally make it a dataframe
  dataframe$z<-0 # i add the variable that i will be returning
  for (i in 1:nrow(dataframe)){
    dataframe$z[i] <- (dataframe$x[i]*(length(which(dataframe$y != dataframe$y[i])))) - sum(dataframe$x[which(dataframe$y != dataframe$y[i])])
    return(dataframe$z)
  }
  return(dataframe$z)
}  
'''

My output is as follows:

 x y   z
1 1 1 -15
2 2 2   0
3 3 3   0
4 4 4   0
5 5 5   0

ideally my output would be: 

 x y   z
1 1 1 -15
2 2 2 -5
3 3 3  0
4 4 4  5
5 5 5  10

CodePudding user response：

It is a case of adding return within the for loop. If we only use the last return, it should work

subtract_within<- function(x,y){ #this function takes in two variables from a dataframe
  dataframe<- data.frame(x,y)  # i locally make it a dataframe
  dataframe$z<-0 # i add the variable that i will be returning
  for (i in 1:nrow(dataframe)){
    dataframe$z[i] <- (dataframe$x[i]*(length(which(dataframe$y != dataframe$y[i])))) - sum(dataframe$x[which(dataframe$y != dataframe$y[i])])
    #return(dataframe$z)
  }
  return(dataframe$z)
}

CodePudding user response：

I think the issue is that you have a return statement inside your loop

for (i in 1:nrow(dataframe)){
    dataframe$z[i] <- (dataframe$x[i]*(length(which(dataframe$y != dataframe$y[i])))) - sum(dataframe$x[which(dataframe$y != dataframe$y[i])])
    return(dataframe$z) # THIS RIGHT HERE
}
return(dataframe$z)

This makes the function immediately return the dataframe after the loop runs only once. If you remove that I think it should work.

for (i in 1:nrow(dataframe)){
    dataframe$z[i] <- (dataframe$x[i]*(length(which(dataframe$y != dataframe$y[i])))) - sum(dataframe$x[which(dataframe$y != dataframe$y[i])])
}
return(dataframe$z)