Merge Two Lists in R

Question

I have two lists  first   list a   1  b   2  c   3  second   list a   2  b   3  c   4    I want to merge these two lists so the final product is    a  1  1 2   b  1  2 3   c  1  3 4   Is there a simple function to do this

User · Accepted Answer

If lists always have the same structure  as in the example  then a simpler solution is  mapply c  first  second  SIMPLIFY FALSE

User · Answer

This is a very simple adaptation of the modifyList function by Sarkar  Because it is recursive  it will handle more complex situations than mapply would  and it will handle mismatched name situations by ignoring the items in  second  that are not in  first    appendList  lt - function  x  val         stopifnot is list x   is list val       xnames  lt - names x      for  v in names val             x  v    lt - if  v  in  xnames  amp  amp  is list x  v     amp  amp  is list val  v                  appendList x  v    val  v            else c x  v    val  v              x     gt  appendList first second   a  1  1 2   b  1  2 3   c  1  3 4

User · Answer

In general one could   merge list  lt - function      by v lt -unlist c       names v  base  c    Note that the by   solution returns an attributed list  so it will print differently  but will still be a list  But you can get rid of the attributes with attr x   attribute name    lt -NULL  You can probably also use aggregate

User · Answer

merged   map names first    c first   x    second   x    merged   set names merged  names first    Using purrr  Also solves the problem of your lists not being in order

User · Answer

Here are two options  the first   both  lt - list first  second  n  lt - unique unlist lapply both  names    names n   lt - n lapply n  function ni  unlist lapply both        ni      and the second  which works only if they have the same structure   apply cbind first  second  1 function x  unname unlist x      Both give the desired result

User · Answer

Here s some code that I ended up writing  based upon  Andrei s answer but without the elegancy simplicity  The advantage is that it allows a more complex recursive merge and also differs between elements that should be connected with rbind and those that are just connected with c     Decided to move this outside the mapply  not sure this is    that important for speed but I imagine redefining the function   might be somewhat time-consuming mergeLists internal  lt - function o element  n element     if  is list n element          Fill in non-existant element with NA elements     if  length n element     length o element          n unique  lt - names n element    names n element   in  names o element         if  length n unique   gt  0           for  n in n unique             if  is matrix n element  n                  o element  n    lt - matrix NA                                        nrow nrow n element  n                                           ncol ncol n element  n                else              o element  n    lt - rep NA                                     times length n element  n                                          o unique  lt - names o element    names o element   in  names n element         if  length o unique   gt  0           for  n in o unique             if  is matrix n element  n                  n element  n    lt - matrix NA                                        nrow nrow o element  n                                           ncol ncol o element  n                else              n element  n    lt - rep NA                                     times length o element  n                                                  Now merge the two lists     return mergeLists o element                         n element          if length n element  gt 1       new cols  lt - ifelse is matrix n element   ncol n element   length n element       old cols  lt - ifelse is matrix o element   ncol o element   length o element       if  new cols    old cols        stop  Your length doesn t match on the elements                 new element     new cols                        old element     old cols               return rbind o element                  n element                  deparse level 0     return c o element              n element     mergeLists  lt - function old  new     if  is null old       return  new     m  lt - mapply mergeLists internal  old  new  SIMPLIFY FALSE    return m      Here s my example   v1  lt - list  a  c 1 2   b  test 1   sublist list one 20 21  two 21 22   v2  lt - list  a  c 3 4   b  test 2   sublist list one 10 11  two 11 12  three 1 2   mergeLists v1  v2    This results in    a        1    2   1      1    2  2      3    4   b  1   test 1   test 2    sublist  sublist one        1    2   1     20   21  2     10   11   sublist two        1    2   1     21   22  2     11   12   sublist three        1    2   1     NA   NA  2      1    2   Yeah  I know - perhaps not the most logical merge but I have a complex parallel loop that I had to generate a more customized  combine function for  and therefore I wrote this monster  -

[r] Merge Two Lists in R

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