R string split and compress empty space

This is supposed to be as simple question but I couldn't figure it out. I'm trying to use a given variables list to choose data variables, however, apply string split I got 8 instead of 5. Clearly, the extra spaces were splited into empty variables for 1,3,5. Any hints on how to solve this?

 list <- " ethnicity_source_value  race_source_value  gender_source_value dx_age site"
  unlist(strsplit(list, " "))
[1] ""                       "ethnicity_source_value" ""                      
[4] "race_source_value"      ""                       "gender_source_value"   
[7] "dx_age"                 "site"   

We could also use str_squish from stringr package; str_squish() also reduces repeated whitespace inside a string:

library(stringr)
unlist(strsplit(str_squish(list), " "))

[1] "ethnicity_source_value" "race_source_value"     
[3] "gender_source_value"    "dx_age"                
[5] "site

The string already had a leading space, so we use trimws to remove those leading/lagging spaces, and then use strsplit with split as one or more spaces (\\s+). It is possible that there are more than a single spaces in between the words.

unlist(strsplit(trimws(list), "\\s+"))
[1] "ethnicity_source_value" "race_source_value"      "gender_source_value"    "dx_age"                
[5] "site"

Or another option is scan which removes the whitespace automatically

scan(text = list, what = "", quiet = TRUE)
[1] "ethnicity_source_value" "race_source_value"      "gender_source_value"    "dx_age"                
[5] "site"