Working with dictionaries lists in R

Question

I have trivial question  I couldn t find a dictionary data structure in R  so I used list instead  like  word - number  So  right now I have problem how to get the list of keys  Anybody knows

User · Answer

You do not even need lists if your  number  values are all of the same mode  If I take Dirk Eddelbuettel s example    gt  foo  lt - c 12  22  33   gt  names foo   lt - c  tic    tac    toe    gt  foo tic tac toe  12  22  33  gt  names foo   1   tic   tac   toe    Lists are only required if your values are either of mixed mode  for example characters and numbers  or vectors   For both lists and vectors  an individual element can be subsetted by name    gt  foo  tac   tac   22    Or for a list    gt  foo   tac     1  22

User · Answer

To extend a little bit answer of Calimo I present few more things you may find useful while creating this quasi dictionaries in R   a  how to return all the VALUES of the dictionary    gt as numeric foo   1  12 22 33   b  check whether dictionary CONTAINS KEY    gt  tic   in  names foo   1  TRUE   c  how to ADD NEW key  value pair to dictionary      c foo tic2 44    results   tic       tac       toe     tic2 12        22        33        44    d  how to fulfill the requirement of REAL DICTIONARY - that keys CANNOT repeat UNIQUE KEYS   You need to combine b  and c  and build function which validates whether there is such key  and do what you want  e g don t allow insertion  update value if the new differs from the old one  or rebuild somehow key e g adds some number to it so it is unique   e  how to DELETE pair BY KEY from dictionary      foo lt -foo which foo  foo   tac

User · Answer

The package hash is now available  https   cran r-project org web packages hash hash pdf  Examples  h  lt - hash  keys letters  values 1 26   h  lt - hash  letters  1 26   h a    1  1 h foo  lt -  bar  h   foo       lt hash gt  containing 1 key-value pair s       foo   bar h    foo        1   bar

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I ll just comment you can get a lot of mileage out of table when trying to  fake  a dictionary also  e g    gt  x  lt - c  a   a   b   b   b   c    gt   t  lt - table x   x a b c  2 3 1   gt  names t   1   a   b   c   gt  o  lt - order as numeric t    gt  names t o    1   c   a   b    etc

User · Answer

Yes  the list type is a good approximation  You can use names   on your list to set and retrieve the  keys     gt  foo  lt - vector mode  list   length 3   gt  names foo   lt - c  tic    tac    toe    gt  foo  1    lt - 12  foo  2    lt - 22  foo  3    lt - 33  gt  foo  tic  1  12   tac  1  22   toe  1  33   gt  names foo   1   tic   tac   toe   gt

User · Answer

The reason for using dictionaries in the first place is performance  Although it is correct that you can use named vectors and lists for the task the issue is that they are becoming quite slow and memory hungry with more data   Yet what many people don t know is that R has indeed an inbuilt dictionary data structure  environments with the option hash   TRUE  See the following example for how to make it work     vectorize assign  get and exists for convenience assign hash  lt - Vectorize assign  vectorize args   c  x    value    get hash  lt - Vectorize get  vectorize args    x   exists hash  lt - Vectorize exists  vectorize args    x      keys and values key lt - c  tic    tac    toe   value  lt - c 1  22  333     initialize hash hash   new env hash   TRUE  parent   emptyenv    size   100L    assign values to keys assign hash key  value  hash     tic tac toe       1  22 333   get values for keys get hash c  toe    tic    hash     toe tic     333   1   alternatively  mget c  toe    tic    hash      toe     1  333         tic     1  1   show all keys ls hash      1   tac   tic   toe    show all keys with values get hash ls hash   hash     tac tic toe      22   1 333   remove key-value pairs rm list   c  toe    tic    envir   hash  get hash ls hash   hash     tac      22   check if keys are in hash exists hash c  tac    nothere    hash         tac nothere        TRUE   FALSE   for single keys this is also possible    show value for single key hash   tac        1  22   create new key-value pair hash   test     lt - 1234 get hash ls hash   hash      tac test       22 1234   update single value hash   test     lt - 54321 get hash ls hash   hash       tac  test        22 54321   Edit  On the basis of this answer I wrote a blog post with some more context  http   blog ephorie de hash-me-if-you-can

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Shorter variation of Dirk s answer     Create a Color Palette Dictionary   gt  color  lt - c  navy blue    gold    dark gray    gt  hex  lt - c   336A91     F3C117     7F7F7F     gt    Create List  gt  color palette  lt - as list hex   gt    Name List Items  gt  names color palette   lt - color  gt    gt  color palette  navy blue  1    336A91    gold  1    F3C117    dark gray  1    7F7F7F

[r] Working with dictionaries/lists in R

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