adding more of they why

modules/Subsetting_Data_in_R/Subsetting_Data_in_R.Rmd

@@ -28,7 +28,7 @@ We are constantly making improvements.
 - The sequence `seq()` function helps you create numeric vectors (`from`,`to`, `by`, and `length.out` arguments)  
 - The repeat `rep()` function helps you create vectors with the `each` and `times` arguments  
 -  Reproducible science makes everyone's life easier!  
-- `readr`has helpful functions like `read_csv()` that can help you import data into R  
+- The `readr` package has helpful functions like `read_csv()` that can help you import data into R  
 
 📃 [Day 2 Cheatsheet](https://daseh.org/modules/cheatsheets/Day-2.pdf)
 
@@ -204,6 +204,14 @@ head(er)
 
 # Renaming Columns
 
+## Why rename?
+
+Renaming can:
+
+- make it easier to work with your data
+- make your column names more compaitible with R
+- make your column names more interpretable by others 
+
 ## `rename` function
 
 ```{r, fig.alt="dplyr", out.width = "70%", echo = FALSE, fig.align='center'}
@@ -414,6 +422,20 @@ C. Keeping it as is and use quotes around the column name when you use it.
 
 # Subsetting Columns
 
+## Why Subset?
+
+Subsetting involves grabbing specific parts of your data to:
+
+- Produce a smaller dataset
+- Examine specific subsets of your data
+- Use a particular part of the data for a specific analysis/visualzation
+
+
+Be cautious about removing columns/variables as you might find they are useful later.
+
+You should be guided by your questions of interest.
+
+
 ## Let's get our data again
 
 We'll work with the CO heat-related ER visits dataset again.