使用R如何保留带有关键字的句子

Question

I have dataset as shown below

   Id     Comments
   1      How. will the binary giant change. 
          Will the unknown disregard maximize another blamed bottle?
   2      The thinking accent hurts.... How.. the lord coast?
   3      The panda moans about the intuitive room past a device.
   4      In an ideology punts the center..
          How. An exercise elaborates past a photographic bookshop

I want to retain sentences that contain the keyword How and not case sensitive

The final dataset should look like this

   Id     Comments
   1      How will the binary giant change. 
   2      How the lord coast?
   3      NA
   4      How An exercise elaborates past a photographic bookshop

Any help is much appreciated.

Answer 1

We can use str_extract

gsub('[.](?!$)', '', 
       str_extract(df1$Comments, "\\bHow.*(\\?|\\.|$)"), perl=TRUE)
#[1] "How will the binary giant change."                       
#[2] "How the lord coast?"                                    
#[3] NA                                                       
#[4] "How An exercise elaborates past a photographic bookshop"