colored array of output

Question

I would like to have colored array of an output. Assume for example we have an array of numbers or texts as output and we want different colors for different classes of them. For example

A={1,2,3,4,5,6,7,8}

and we want Odd numbers be Blue and Even numbers be Red.

or

PrimeQ[A] which gives True or False, with Blue color for True and Red color for False.

Thanks.

Answer 1

First approach

Function to change the style of elements of a specific class in an expression.

Code.

SetAttributes[coloredreplace, HoldAllComplete];

coloredreplace[expr_, testQ_, colors: {True -> c1_?ColorQ, False -> c2_?ColorQ}] := 
    coloredreplace[expr, {Sequence[], testQ}, colors];

coloredreplace[expr_, {head_, testQ_}, {True -> c1_?ColorQ, False -> c2_?ColorQ}] := 
    Replace[expr, {n_head?testQ :> Style[n, c1], n_head :> Style[n, c2]}, {1}];

Usage.

1) For EvenQ elements:

expr1 = Range[8];

coloredreplace[expr1, EvenQ, {True -> Red, False -> Blue}]

% === coloredreplace[expr1, {Integer, EvenQ}, {True -> Red, False -> Blue}]
(* True *)

2) For PrimeQ elements:

coloredreplace[expr1, {Integer, PrimeQ}, {True -> Blue, False -> Red}]

3) For elements satisfying a StringMatchQ test:

expr2 = {"a", "1", 1, "b", "2", 2, "c", "3", 3};

coloredreplace[expr2, StringMatchQ[#, LetterCharacter] &, {True -> Red, False -> Blue}]

We can specify the head to get a cleaner pattern:

coloredreplace[expr2, {String, StringMatchQ[#, LetterCharacter] &}, 
                      {True -> Red, False -> Blue}
]

This removed the messages and changed the display for non-String elements.

Second approach

Function to define global rules of display for elements of a specific class.

Code.

coloreddisplay[{head_, testQ_}, {True -> c1_?ColorQ, False -> c2_?ColorQ}] :=
    Module[{},

        FormatValues[MakeBoxes] = DeleteCases[FormatValues[MakeBoxes],
            HoldPattern[
                Verbatim[HoldPattern][MakeBoxes[
                   Verbatim[PatternTest][Verbatim[Pattern][_, Verbatim[Blank][head]], _], 
                   StandardForm
                ]] :> 
                RowBox[{StyleBox[_, color_]}]
            ] /; ColorQ[color]
        ];

        MakeBoxes[n_head?testQ, StandardForm] := RowBox[{StyleBox[n, c1]}];
        MakeBoxes[n_head, StandardForm] := RowBox[{StyleBox[n, c2]}];

    ];

Usage.

coloreddisplay[{Integer, EvenQ}, {True -> Red, False -> Blue}];

expr1

coloreddisplay[{Integer, PrimeQ}, {True -> Blue, False -> Red}];

expr1

coloreddisplay[{String, StringMatchQ[#, LetterCharacter] &}, {True -> Red, False -> Blue}]

expr2

The digits 1, 2 and 3 are colored because the rule for PrimeQ elements define previously still applies. Removing all rules generated by coloreddisplay can be simply done with FormatValues[MakeBoxes] = {}, which could be written in its code instead of the DeleteCases part if needed. Note that this will also delete MakeBoxes rules defined elsewhere.