How do I create multiple dataframes using a loop by separating an existing dataframe by a variable

Question

I have data that is like the following (Except that is populated by all 52 weeks). "data"

Week   State    Value 
1        CA      4
1        AL      5
1        MO      9
1        IL      12
2        NY      1
2        CA      2
2        WA      8
3        WY      9
3        SC      10

I would like to create new data.frames for every week so that I may do further analyses. How would I go about this? I tried:

for( i in 1:52) {
     DataWeeki <- data[which(data$Week==i),]
}

This creates a single dataframe of 3 variables (with the appropriate variable names) but no data.

What is the correct way to go about this?

Answer 1

We can use split in base R to create a list of data.frames

lst1 <- split(data, data$Week)
names(lst1) <- paste0("DataWeek", 1:52)

From the list, elements can be extracted with $ or [[

lst1[["DataWeek1"]]

It is not recommended to create multiple objects in the global environment, but if we need, we can use list2env (but there would be 52 objects and not good at all)

 list2env(lst1, .GlobalEnv)

---

Regarding why it creates a single object is because the object gets updated in each run and what we get is the last run object. Instead, here assign is needed (not recommended)

for( i in 1:52) {
   assign(paste0("DataWeek", i), data[which(data$Week==i),])
 }

lists can also be created with for loop

lst1 <- vector("list", 52)
for(i in 1:52) {
       lst1[[i]] <- data[which(data$Week==i),]
  }