included examples

Author: venom1204

vignettes/datatable-joins.Rmd

@@ -702,7 +702,7 @@ Products[!"popcorn",
 
 Use `:=` to modify columns **by reference** (no copy) during joins. General syntax: `x[i, on=, (cols) := val]`.
 
-- Simple One-to-One Update  
+**Simple One-to-One Update**  
 Update `Products` with prices from `ProductPriceHistory`:
 
 ```{r}
@@ -713,7 +713,7 @@ Products[ProductPriceHistory,
 - i.price refers to price from i (ProductPriceHistory).
 - Modifies Products in-place.
 
-- Grouped Updates with `.EACHI`
+**Grouped Updates with `.EACHI`**
 Get last price/date for each product:
 ```{r Updating_with_the_Latest_Record}
 Products[ProductPriceHistory,
@@ -727,7 +727,7 @@ Products[ProductPriceHistory,
 ```{r}
 data.table::last(c(1, NA))  # NA
 ```
--  Efficient Right Join Update
+**Efficient Right Join Update**
 Add product details to ProductPriceHistory without copying:
 
 ```{r}
@@ -738,9 +738,39 @@ ProductPriceHistory[, (cols) :=
 - .SD refers to ProductPriceHistory during the join.
 - Updates ProductPriceHistory by reference.
 
-- last(x) vs tail(x,1): Both return last element, but tail() returns list for lists.
-- := always modifies x, never i. For right joins, update i directly via i[, ... := x[.SD]].
-- .EACHI is crucial for per-row operations; simple joins use first match.
+**Handling Edge Cases and Dynamic Column Updates**
+To dynamically update columns and handle missing values:
+```{r}
+cols <- setdiff(names(Products), "id")
+ProductPriceHistory[, (cols) := 
+  Products[.SD, on = .(id = product_id), .SD, .SDcols = cols]]
+ProductPriceHistory[is.na(price), price := 0]  # Handle missing values
+```
+- Ensures unmatched values do not propagate `NA` unintentionally.
+
+**Dynamic Column Selection and Updates**
+Columns can be dynamically updated based on variable names:
+```{r}
+my_var_name <- "price"
+Products[ProductPriceHistory, on = .(id = product_id), 
+         (my_var_name) := i.price]
+```
+- This approach allows flexibility in specifying columns programmatically.
+
+**Iterating Through Multiple Columns for Updates**
+Dynamically updating multiple columns from `ProductPriceHistory`:
+```{r}
+update_cols <- intersect(c("price", "category", "stock"), names(ProductPriceHistory))
+
+for (col in update_cols) {
+  Products[ProductPriceHistory, on = .(id = product_id), (col) := get(paste0("i.", col))]}
+```
+- Ensures multiple columns are updated efficiently in a loop.
+
+**Summary**
+- `last(x)` vs `tail(x,1)`: Both return last element, but `tail()` returns list for lists.
+- `:=` always modifies `x`, never `i`. For right joins, update `i` directly via `i[, ... := x[.SD]]`.
+- `.EACHI` is crucial for per-row operations; simple joins use first match.
 
 ***