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Ok. I'm obviously not understanding something about pattern matching.

I have a list called t like the following:

t = {{3.2,5.9,Indeterminate},{4.5,-3 - 100 (1 - 2/(Underflow[] + 1)) + 200 (1 - Underflow[]),7.9},{1.2,9.1,2.3}}

Where I would like to use ReplaceAll[] to convert all non-real values to 0.0, like so:

{{3.2,5.9,0.0},{4.5,0.0,7.9},{1.2,9.1,2.3}}

How could I do this with ReplaceAll[] and pattern matching?

I have tried:

t /. r_ /; Head[r] != List | Real -> 0.0

But that does nothing to the list. I am trying to wrap my head around pattern matching, but I'm not quite there yet, and any help would be greatly appreciated.

Thanks!

P.S.- I would really like to understand this in context of pattern matching, but other more efficient ways of doing this are also appreciated!

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5 Answers 5

7
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You had two issues.

  1. You can't use Unequal ("!=") with Alternatives ("|").
  2. Even if you correct your pattern, the pattern would match the whole expression.

Using Replace with a level spec and a corrected pattern:

t = {{3.2,5.9,Indeterminate},{4.5,-3-100 (1-2/(Underflow[]+1))+200 (1-Underflow[]),7.9},{1.2,9.1,2.3}};

Replace[
    t,
    r_ /; !MatchQ[Head[r], List | Real] -> 0.0,
    {2}
]

{{3.2, 5.9, 0.}, {4.5, 0., 7.9}, {1.2, 9.1, 2.3}}

Another possibility:

Replace[
    t,
    Except[_?NumberQ] -> 0.,
    {2}
]

{{3.2, 5.9, 0.}, {4.5, 0., 7.9}, {1.2, 9.1, 2.3}}

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  • $\begingroup$ Great, thanks! That helps me to understand it a lot better $\endgroup$
    – Jmeeks29ig
    Sep 20, 2018 at 1:00
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I prepended 11, 1/3 and 4 + 3 I to the first sublist

list =
  {{11, 1/3, 4 + 3 I, 3.2, 5.9, Indeterminate},
   {4.5, -3 - 100 (1 - 2/(Underflow[] + 1)) + 200 (1 - Underflow[]), 7.9},
   {1.2, 9.1, 2.3}};

1.

RealValuedNumberQ (new in 13.3) gives, in my opinion, the best solution (according to the title of the question)

Replace[list, Except[_?RealValuedNumberQ] -> 0., {2}]

{{11, 1/3, 0., 3.2, 5.9, 0.}, {4.5, 0., 7.9}, {1.2, 9.1, 2.3}}

2.

This replaces 11 and 1/3 (which are real numbers)

Replace[list, x_ /; Head[x] =!= Real -> 0., {2}]

{{0., 0., 0., 3.2, 5.9, 0.}, {4.5, 0., 7.9}, {1.2, 9.1, 2.3}}

3.

This doesn't replace 4 + 3 I

Replace[list, Except[_?NumberQ] -> 0., {2}]

{{11, 1/3, 4 + 3 I, 3.2, 5.9, 0.}, {4.5, 0., 7.9}, {1.2, 9.1, 2.3}}

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list = {{3.2, 5.9, Indeterminate}, {4.5, -3 - 100 (1 - 2/(Underflow[] + 1)) + 
         200 (1 - Underflow[]), 7.9}, {1.2, 9.1, 2.3}};

Using Cases and If:

Cases[#, x_ :> If[MatchQ[x, _?NumberQ], x, 0.]] & /@ list

(*{{3.2, 5.9, 0.}, {4.5, 0., 7.9}, {1.2, 9.1, 2.3}}*)
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list = 
 {{3.2, 5.9, Indeterminate}, 
  {4.5, -3 - 100 (1 - 2/(Underflow[] + 1)) + 200 (1 - Underflow[]), 7.9}, 
  {1.2, 9.1, 2.3}};

Using ReplaceAt (new in 13.1)

ReplaceAt[list, Except[_Real] :> 0.0, {All, All}]

{{3.2, 5.9, 0.}, {4.5, 0., 7.9}, {1.2, 9.1, 2.3}}

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With some extra levels added for testing:

list = {{3.2, 5.9, 
    Indeterminate}, {{{{4.5, -3 - 100 (1 - 2/(Underflow[] + 1)) + 
        200 (1 - Underflow[]), 7.9}}, {1.2, 9.1, 2.3}}}};

list /. a_?VectorQ :> SequenceReplace[a, {Except[_Real]} :> 0.0]

{{3.2, 5.9, 0.}, {{{{4.5, 0., 7.9}}, {1.2, 9.1, 2.3}}}}

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