Update wrangling_practical.md

IntroR_practical_online_resource/wrangling_practical.md

@@ -22,9 +22,9 @@
 
 2. We have obtained batch information for the control samples in this dataset. **Copy and paste the code below to create a dataframe of control samples with the associated batch information**:
 
-```
-ctrl_samples <- data.frame(row.names = c("sample3", "sample10", "sample8", "sample4", "sample15"), date = c("01/13/2018", "03/15/2018", "01/13/2018", "09/20/2018","03/15/2018"))
-```
+  ```
+  ctrl_samples <- data.frame(row.names = c("sample3", "sample10", "sample8", "sample4", "sample15"), date = c("01/13/2018", "03/15/2018", "01/13/2018", "09/20/2018","03/15/2018"))
+  ```
 
 3. How many of the `ctrl_samples` are also in the `proj_summary` dataframe? Use the %in% operator to compare sample names.
 4. Keep only the rows in `proj_summary` which correspond to those in `ctrl_samples`. Do this with the %in% operator. Save it to a variable called `proj_summary_ctrl`.