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I have a badly structured data and I need to clean it up, suppose I have the following list: 

l={{"a","b","c"},{"e"," f","g"},{" a"," b"}}

As you can see they are string, yet some are having an extra Space, instead of being "a" for example it is " a" I was wondering how one deletes those extra spaces to achieve the right format of data. I have tried StringTrim[] but it seems it does not work on a list?

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2
  • 3
    $\begingroup$ Map[StringTrim, l, {-1}] $\endgroup$
    – Kuba
    Commented Jul 27, 2018 at 14:08
  • 3
    $\begingroup$ StringTrim/@l ?? $\endgroup$
    – murray
    Commented Jul 27, 2018 at 14:10

2 Answers 2

Reset to default
6
$\begingroup$ 
StringReplace[#, " " -> ""] & /@ l

{{"a", "b", "c"}, {"e", "f", "g"}, {"a", "b"}}

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$\begingroup$

With a larger string list

l = With[
   {size = 100},
   MapAt[
    StringJoin[" ", #, " "] &,
    RandomChoice[CharacterRange["a", "z"], {size, size}],
    RandomInteger[{1, size}, {size, 2}]
    ]];

My own

First@RepeatedTiming[ 
  StringDelete[" "] /@ l
  ]
(* 0.000750 *)

@murray

First@RepeatedTiming[ 
  StringTrim /@ l
  ]
(* 0.00497 *)

@Coolwater

First@RepeatedTiming[
  StringReplace[#, " " -> ""] & /@ l
  ]
(* 0.000801 *)

@Coolwater operator mode

First@RepeatedTiming[
  StringReplace[" " -> ""] /@ l
  ]
(* 0.000757 *)

@Kuba

First@RepeatedTiming[
  Map[StringTrim, l, {-1}]
  ]
(* 0.0482 *)
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  • 1
    $\begingroup$ Interestingly, I found ParallelMap is much slower than Map (3 - 18x slower) for all except the last command (where it was 2x faster). I didn't play with the coarseness options. [Since I was using Parallelize, I benchmarked using wall clock (with AbsoluteTime[]), and a single run with size = 2000, rather than RepeatedTiming with size = 100.] $\endgroup$
    – theorist
    Commented Jul 27, 2018 at 17:55
  • 1
    $\begingroup$ @theorist RepeatedTiming is supposed to be more reliable. Sometimes a particular calculation slows down because the OS may be doing unrelated stuff, and you want to remove the outliers, but I agree that I chose an unnecessarily small number for the data size. $\endgroup$
    – rhermans
    Commented Jul 27, 2018 at 17:58
  • $\begingroup$ Need to confirm RepeatedTiming uses wall clock rather than CPU time, since the former is needed to get meaningful comparisons when parallelizing; found it does :). I then repeated the comparison using RepeatedTiming, with size = 100, using a 5-second duration to improve accuracy. I found ParallelMap took longer, for the above commands, by factors of 21, 3.5, 19, 21, and 1.3, respectively—roughly the same results I got with a single run of size = 2000 with AbsoluteTiming, except for the last command, which was also now slower with ParallelMap (perhaps b/c of the diff. in size). $\endgroup$
    – theorist
    Commented Jul 27, 2018 at 18:47

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