> # set names to the states vector
> us_states = setNames(state.name, state.abb)
> us_states
              AL               AK               AZ               AR               CA
       "Alabama"         "Alaska"        "Arizona"       "Arkansas"     "California"
              CO               CT               DE               FL               GA
      "Colorado"    "Connecticut"       "Delaware"        "Florida"        "Georgia"
              HI               ID               IL               IN               IA
        "Hawaii"          "Idaho"       "Illinois"        "Indiana"           "Iowa"
              KS               KY               LA               ME               MD
        "Kansas"       "Kentucky"      "Louisiana"          "Maine"       "Maryland"
              MA               MI               MN               MS               MO
 "Massachusetts"       "Michigan"      "Minnesota"    "Mississippi"       "Missouri"
              MT               NE               NV               NH               NJ
       "Montana"       "Nebraska"         "Nevada"  "New Hampshire"     "New Jersey"
              NM               NY               NC               ND               OH
    "New Mexico"       "New York" "North Carolina"   "North Dakota"           "Ohio"
              OK               OR               PA               RI               SC
      "Oklahoma"         "Oregon"   "Pennsylvania"   "Rhode Island" "South Carolina"
              SD               TN               TX               UT               VT
  "South Dakota"      "Tennessee"          "Texas"           "Utah"        "Vermont"
              VA               WA               WV               WI               WY
      "Virginia"     "Washington"  "West Virginia"      "Wisconsin"        "Wyoming"