library(stringr)
url_pattern <- "http[s]?://(?:[a-zA-Z]|[0-9]|[$-_@.&+]|[!*(),]|(?:%[0-9a-fA-F][0-9a-fA-F]))+"
data$ContentURL <- str_extract(data$Content, url_pattern)
data
## Content date ContentURL
## 1 a house a home https://www.foo.com 12/31/2013 https://www.foo.com
## 2 cabin ideas https://www.example.com in the woods 5/4/2013 https://www.example.com
## 3 motel is a hotel 1/4/2013 <NA>