How to I overcome Dividing by Zero Error in R - sql

Question

Hi, Stack community! I came across this error working today. I am not sure exactly how to work around it. I read to use a na.rm in my mutate, and I tried it, but it didn't work. I could be completely wrong.
library("DBI")
library("dbplyr")
library("odbc")
library("dplyr")
library("stringr")
library("tidyverse")
library("lubridate")
select(CustomerID, PostalCodeID, OrderID, ItemID, WrittenSales, WrittenUnits, TransCodeID, SalesType, ProductID, ProductName, GroupID, SubGroupID, CategoryID, TransDate, LocationID, LocationName) %>%
filter(SalesType == "W",
LocationID %in% Louisville) %>%
group_by(CustomerID, PostalCodeID, WrittenSales, TransCodeID, SalesType, ProductID, ProductName, GroupID, SubGroupID, CategoryID, TransDate, LocationID, LocationName) %>%
summarise(WrittenUnits_purchased = sum(WrittenUnits)) %>%
ungroup() %>%
group_by(CustomerID) %>%
mutate(prop_of_total = WrittenUnits_purchased/sum(WrittenUnits_purchased)) %>%
ungroup()```

Answer 1

While this is a SQL problem, it can be mitigated in your code.
Setup:
# library(odbc) or similar, for the DB driver
# con <- DBI::dbConnect(...)
DBI::dbExecute(con, "create table r2 (x int, y int)")
# [1] 0
DBI::dbExecute(con, "insert into r2 (x,y) values (1,1),(2,0)")
# [1] 2
DBI::dbGetQuery(con, "select * from r2")
# x y
# 1 1 1
# 2 2 0
Demonstration of the problem in base R, and the SQL-based fix:
DBI::dbGetQuery(con, "select x/y as xy from r2")
# Error in result_fetch(res#ptr, n) :
# nanodbc/nanodbc.cpp:2593: 22012: [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Divide by zero error encountered.
# Warning in dbClearResult(rs) : Result already cleared
DBI::dbGetQuery(con, "select (case when y = 0 then null else x/y end) as xy from r2")
# xy
# 1 1
# 2 NA
Since you're using dbplyr, here's that side of things:
library(dplyr)
library(dbplyr)
tbl(con, "r2") %>%
collect()
# # A tibble: 2 x 2
# x y
# <int> <int>
# 1 1 1
# 2 2 0
tbl(con, "r2") %>%
mutate(xy = x/y) %>%
collect()
# Error in result_fetch(res#ptr, n) :
# nanodbc/nanodbc.cpp:2593: 22012: [Microsoft][ODBC Driver 17 for SQL Server][SQL Server]Divide by zero error encountered.
# Warning in dbClearResult(res) : Result already cleared
tbl(con, "r2") %>%
mutate(xy = if_else(y == 0, NA, x/y)) %>%
collect()
# # A tibble: 2 x 3
# x y xy
# <int> <int> <int>
# 1 1 1 1
# 2 2 0 NA