I have a list of names in which I would like to check for duplicates. However, within the list, the duplicates may not show up as exact duplicates of each other - for instance,

{Barack Obama, Barack H. Obama, Barack Hussein Obama, Obama Barack Hussein}

are all considered likely candidates to be duplicates of each other. Furthermore, the data may contain slight mistakes - for instance, the following and other variants would be considered (near) duplicates too.

{Barack Obama, barack Obama, Barrack Obama}

What I would like to do is to automatically highlight these duplicates (for example, by changing their font size or color as displayed on screen) so that I can later go through the list manually and confirm whether or not the duplicates are indeed duplicates.

My current approach is as such:

nlsplit = 
StringSplit /@ namelist; (*splitting the names at the whitespace*)
nlsplitsort = 
Map[Sort, nlsplit, 
2] ; (*sorting the names of each person alphabetically - for
example, John Anderson Doe becomes {Anderson, Doe, John}*)
nlsplitsortpad = Transpose[Map[PadRight[#, 5] &, nlsplitsort, 2]][[1]];
(*pad each person's name with zeros so that Mathematica doesn't sort
based on list length but on name*)

This question may be linked to mine, but I feel it's sufficiently different to merit a post. Mr Wizard also informed me that a question of Soft-Match String Comparison may have been asked before and the link is here as Sjoerd C. de Vries points out.

Edit: It would be great if the following could be done, but from my knowledge of Mathematica, I'm not sure whether it's worth the effort.

  1. The process of highlighting duplicates does not change the ordering of the original list, but simply highlights them, and
  2. I could simply hover over a duplicate candidate where using Tooltip we display the possible matches identified as similar to this duplicate candidate.
  3. By choosing from a list of options I could do one of the following:
    • select the current duplicate candidate as the entry I want to keep (and remove all other similar candidates from the main list)
    • skip to one of the other matches displayed by the Tooltip and choose that as the entry I want to keep (removing all other similar candidates from the main list)
    • confirm that the current candidate is not in fact a duplicate, and remove it from the list of any candidate of duplicates.
  • 1
    $\begingroup$ Possible duplicate: how-to-perform-fuzzy-lookup-between-lists $\endgroup$ Mar 4, 2013 at 15:04
  • $\begingroup$ thank you, perhaps that's what Mr Wizard was talking about. $\endgroup$ Mar 4, 2013 at 15:12
  • $\begingroup$ @Sjoerd Thanks; that indeed is the one. Vincent, you might reformulate this question to emphasize the part about highlighting (near) duplicates rather than about finding them; that should keep this question open. $\endgroup$
    – Mr.Wizard
    Mar 4, 2013 at 15:21

3 Answers 3


Start by making some similarity measure of sentences, here I use one that takes number of words in common divided by number of words in longest sentence.

The measure is then used to connect sentences that are similar enough in a graph and extracts the connected components:

strs = {"Barack Obama", "Barack H. Obama", "Barack Hussein Obama", 
        "Obama Barack Hussein", "Barrack Obma", "Some other", "Strings", 
        "That are not duplicates","NotReally Barrack Obama"};
sameWordQ[w1_, w2_] := EditDistance[w1, w2, IgnoreCase->True] < 2;
similarity[str1_, str2_] := Module[{
   l1 = StringSplit[str1],
   l2 = StringSplit[str2]},
  Length@Intersection[l1, l2,SameTest->sameWordQ]/Max[Length[l1], Length[l2]]
findDupes[lst_] := ConnectedComponents@Graph@Flatten@MapIndexed[
     Function[{str, ind},
       Thread[str \[UndirectedEdge] Select[lst[[First@ind ;;]], similarity[str, #] >= 2/3 &]]
     ], lst]

(* {{"Barack Obama", "Barack H. Obama", "Barack Hussein Obama", 
    "Obama Barack Hussein", "Barrack Obma", "NotReally Barrack Obama"},
    {"Some other"}, {"Strings"}, {"That are not duplicates"}} *)

To actually answer the question and visually verify the output and remove false positives:

For each group returned take away all groups of length 1. Then for each name create a button that lets you remove a name if it is considered a false positive.

Options[verifyDupes] = {HoldFirst};
(* When you click save the result is stored in the first argument *)
verifyDupes[result_Symbol, dupes_] := 
   groups = Select[dupes, Length@# > 1 &],
   isDupe = Blue, notDupe = Black, styles},

  (*Creata a list of same size where each element is marked a duplicate*)
  styles = Map[isDupe &, groups, {2}];

    MapIndexed[Function[{str, ind}, 
      Button[Dynamic[Style[str, styles[[Sequence @@ ind]]]],
       (*Switch style when a name is clicked*)
       styles[[Sequence @@ ind]] = If[styles[[Sequence @@ ind]] === isDupe, notDupe,isDupe], 
       Appearance -> None]], groups, {2}],
     (*Remove all names that have been deselected*)
     result = MapIndexed[
       If[styles[[Sequence @@ #2]] === isDupe, #1, Unevaluated@Sequence[]] &,
       groups, {2}]]}

strs = {"Barack Obama", "Barack H. Obama", "Barack Hussein Obama", 
 "Obama Barack Hussein", "barrack obma", "Some other", "Strings", 
 "That are not duplicates", "NotReally Barack Obama",
 "John Anderson Doe", "John A. Doe", "John Doe"};



  • $\begingroup$ What about words that are misspelled but can be expected to be the same? (e.g. Barrack Obama) Sorry I didn't mention this in the original. $\endgroup$ Mar 4, 2013 at 15:10
  • $\begingroup$ @VincentTjeng Modify the similarity function to take (for instance) hamming distance into account. $\endgroup$
    – ssch
    Mar 4, 2013 at 15:11
  • $\begingroup$ @VincentTjeng Updated the answer just as you commented :) $\endgroup$
    – ssch
    Mar 4, 2013 at 15:25
  • $\begingroup$ sorry for the late accept :) $\endgroup$ Mar 12, 2013 at 6:11

Since Mathematica 6, there are a few integrated algorithms for computing the difference between strings, for example EditDistance, DamerauLevenshteinDistance (see also http://en.wikipedia.org/wiki/Approximate_string_matching), HammingDistance, and SmithWatermanSimilarity.

Here's a quick and dirty implementation how to make use of these algorithms:

MarkSimilarStrings[stringlist_List] := 
Module[{similarityScores, SimilarThreshold = 10, 
    SimilarityFunc = EditDistance, comps},

    CheckForSimilarity[string1_, string2_] := 
    If[SimilarityFunc[string1, string2] < SimilarThreshold, similarityScores[string2] += 1];

    Scan[(similarityScores[#] = 0) &, stringlist];

    Outer[CheckForSimilarity, stringlist, stringlist];
    Print[Map[Print[similarityScores[#]] &, stringlist]];

    Map[If[similarityScores[#] > 2, Style[#, FontColor -> Red], #] &, stringlist]

This function takes a string list as argument and puts out a list with the suspected duplicates in red. It is crucial here to understand how the algorithms like EditDistance[] (for Levenshtein distance) work to figure out a useful value for SimilarThreshold. I suggest playing around a bit.

  • 2
    $\begingroup$ Hi Ulrik, I added some links. Remove them if you like. Or keep them. Hope you don't mind. David $\endgroup$
    – DavidC
    Mar 4, 2013 at 15:56
  • $\begingroup$ I don't :) Thanks for the links! $\endgroup$ Mar 4, 2013 at 16:01

To highlight newer possibilities in Mathematica that have been added since featuring the Entity system:

strs = {"Barack Obama", "Barack H. Obama", "Barack Hussein Obama", 
   "Obama Barack Hussein", "Barrack Obma", "Some other", "Strings", 
   "That are not duplicates", "NotReally Barrack Obama"};

{#, Interpreter["ComputedPerson"][#]} & /@ strs /. _Failure :> 
   "No Interpretation" // Grid

enter image description here


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.