将文本附加到数据框中的列的最佳方法是什么？

Question

I have a column in my data frame that has date data in it:

> head(df$postedDate_strip2,n = 20)
 [1] NA                   "November 13, 2014" 
 [3] "September 27, 2014" "October 8, 2014"   
 [5] "December 16, 2013"  "February 8"        
 [7] "November 2, 2014"   "November 30, 2014" 
 [9] "February 18"        "August 22, 2014"   
[11] "October 26, 2014"   "January 3, 2014"   
[13] "February 3, 2014"   "October 15, 2014"  
[15] "September 12, 2014" "May 5"             
[17] "April 2, 2014"      "November 4, 2014"  
[19] "January 16, 2014"   "September 28, 2014"

All the 2015 data don't have the , 2015 text at the end. Is there a recommended way to simply append ", 2015" to entries that don't contain a comma?

Answer 1

gsub("(^[^,]+$)", "\\1, 2015", x)
#[1] "December 16, 2013" "February 8, 2015"  "November 2, 2014" 
#[4] NA                  "February 18, 2015"

Regex makes the task easier. The pattern "(^[^,]+$)" Checks for strings without a comma and replaces it with the same string with the year appended. Using the anchors ^ and $ are vital to the search. The first matches the first position in the string, the latter matches the last position.