How to search a list for all the words with two of a certain letter in it?

Question

In Rstudio, how can I obtain all the words that have two of a particular letter in them using the below-mentioned function:

1. grep/grepl 
2. sub/gsub

Answer 1

See if you want to get the states with two or more "a"s in them, then in that case use :

grep('.*a.*a.*', state.name, value = TRUE, ignore.case = TRUE)

The output in R programming will be:

# [1] "Alabama"        "Alaska"         "Arizona"        "Arkansas"      

# [5] "California"     "Delaware"       "Hawaii"         "Indiana"       

# [9] "Kansas"         "Louisiana"      "Maryland"       "Massachusetts" 

#[13] "Montana"        "Nebraska"       "Nevada"         "North Carolina"

#[17] "North Dakota"   "Oklahoma"       "Pennsylvania"   "South Carolina"

#[21] "South Dakota"  

And let say, you want exactly two "a"s, what you can do is use the str_count to count the number of "a"s and then perform the subsetting.

state.name[stringr::str_count(state.name, 'a|A') == 2]

# [1] "Arizona"        "California"     "Delaware"       "Hawaii"        

# [5] "Indiana"        "Kansas"         "Louisiana"      "Maryland"      

# [9] "Massachusetts"  "Montana"        "Nebraska"       "Nevada"        

#[13] "North Carolina" "North Dakota"   "Oklahoma"       "Pennsylvania"  

#[17] "South Carolina" "South Dakota"