Using for loop to get a list data frames in R

Question

splitted is a list of data frames coming from a split() on the main data frame.

After splitting, I'm applying a function to every data frame in the splitted list.

Here the function:

getCustomer <- function(df, numberOfProducts = 3){

Gender <- unique(df$gender)
Segment <- unique(df$Segment)
Net_Discount <- sum(df$Discount * df$Sales)
Number_of_Discounts <- sum(df$Discount>0)
Customer.ID <- unique(df$Customer.ID)
Sales <- sum(df$Sales)
Profit <- sum(df$Profit)
lat <- mean(df$lat)
lon <- mean(df$lon)

productsData <- df %>% arrange(Order.Date) %>% top_n(n =numberOfProducts)

Products <- 0 
Products_Category <- 0
Products_Order_Date <- 0

for (j in 1:numberOfProducts){ 

Products[j] <- productsData %>% select(Product.ID) %>% filter(row_number()==j)
Products_Category[j] <- productsData %>% select(Category) %>% filter(row_number()==j)
  Products_Order_Date[j] <- productsData %>% select(Order.Date) %>% filte(row_number()==j)

  names(Products)[j]<-paste("Product",j)
  names(Products_Category)[j]<-paste("Category Product",j)
  names(Products_Order_Date)[j]<-paste("Order Date Product",j)

  }


  output <- data.frame(Customer.ID, Gender,Segment, Net_Discount, Number_of_Discounts, Sales, Profit, 
                   Products, Products_Category, Products_Order_Date, lon,lat)

return(output[1,])
}

I get the right answer for any element of splitted

getCustomer(splitted[[687]],2)

I can even do well with

customer <- list()
customer[[1]]<- getCustomer(splitted[[1]],2)
customer[[2]]<- getCustomer(splitted[[2]],2)
.
.
.
customer[[1576]]<- getCustomer(splitted[[1576]],2)

That is, I can effectively build the whole customer list by assigning element by element.

However, I certainly don't have time for that (1576 single line data frames to assign to the customer list), so I'm trying:

customer <- list()

for (i in 1:length(splitted)){

  customer[[i]]<-getCustomer(splitted[[i]],2)

}

After running this last chunk of code, I get:

Error in data.frame(Customer.ID, Gender,  Segment, Net_Discount, Number_of_Discounts, : arguments imply differing number of rows: 0, 1

I can't understand this error, since I can build the customer list element by element at a time.

Would apreciate your help.

Solution

Editing this question to let you know the problem was indeed that some data frames in splitted had no rows. So I removed them (only 3).

for (i in 1:length(splitted)){
l[i]<-nrow(splitted[[i]])  
}

indices<- which(l==0)

splitted<-splitted[-indices]

Just had to delete 3 samples. Got no error this time. Thank you all for your time.

Tim Biegeleisen · Accepted Answer · 2018-05-16 02:31:30Z

1

Just use lapply, which can apply a function to every element of a list, returning a list in the process:

numberOfProducts <- 2
result <- lapply(splitted, function(x) getCustomer(x, numberOfProducts))

Edit:

It looks like your function has logic which sometimes can result in a data frame with no rows. In this case, you may check for an empty data frame and return NA:

output <- data.frame(Customer.ID, Gender,Segment, Net_Discount, Number_of_Discounts, Sales,
    Profit, Products, Products_Category, Products_Order_Date, lon, lat)
return(ifelse(nrow(output) > 0, output[1,], NA))

edited May 16, 2018 at 2:31

answered May 16, 2018 at 2:12

Tim Biegeleisen

526k32 gold badges324 silver badges399 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Tim Biegeleisen Over a year ago

@AndrésAcostaEscobar The real problem then is that you are sometimes trying to return the first row of an empty data frame. Check your data and logic.

Andrés Acosta Escobar · Accepted Answer · 2018-05-16 03:40:31Z

1

The problem was indeed that some data frames in splitted had no rows. So I removed them (only 3).

for (i in 1:length(splitted)){
l[i]<-nrow(splitted[[i]])  
}

indices<- which(l==0)

splitted<-splitted[-indices]

Just had to delete 3 samples.

Got no error this time. Thank you all for your time.

edited May 16, 2018 at 3:40

answered May 16, 2018 at 3:17

Andrés Acosta Escobar

811 gold badge1 silver badge7 bronze badges

Comments

Melissa Key · Accepted Answer · 2018-05-16 02:37:16Z

My usual strategy for troubleshooting something like this is to start running it in chunks. If you use the for loop, check what value of i is when the error occurs. With lapply, I will run in chunks of around 20... and keep going until you find which data frame in your list is causing the error.

Then, run through your function manually with that data frame and look at what output you get. For example:

df <- splitted[[30]] # assuming #30 is the problem
numberOfProducts <- 3

now walk through the function arguments and check that output until you find what causes the error. Keep in mind that if there are multiple places where problems can occur, it might take more than one application of this process to solve all the problems.

Collectives™ on Stack Overflow

Using for loop to get a list data frames in R

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related