How to assign specific value for character

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wesleynotwise 2017-5-21

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评论： Walter Roberson 2017-5-22

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I have a cell array of character vectors, let say

A = {'r' 'b' 'g'; 'g' 'r' 'b'; 'b' 'r' 'g'}

how do I change this character to a specific value, eg: r = 0.5, b = 2, g = -3?

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Answer 1

Jos (10584) 2017-5-21

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Here is an easy way:

A = {'r' 'b' 'g'; 'g' 'r' 'b'; 'b' 'r' 'g'}
RGBval = [0.5 2 -3]
[~,loc] = ismember(A,{'r','g','b'})
B = RGBval(loc)

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wesleynotwise 2017-5-21

编辑：wesleynotwise 2017-5-21

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Thanks. I am thinking to use the following command, but of course it is incorrect because the output is categorical array. Any idea how to correct it?

B = categorical(A,{'r' 'g' 'b'},{'0.5' '2' '-3'})

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Answer 2

Walter Roberson 2017-5-21

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RGBval('rgb') = [0.5 2 -3];
A = {'r' 'b' 'g'; 'g' 'r' 'b'; 'b' 'r' 'g'};
B = cellfun(@(C) RGBval(C), A);

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wesleynotwise 2017-5-22

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Sorry. Can you explain what is

RGBval('rgb') = [0.5 2 -3]

It generates a 1x114 double output?

Walter Roberson 2017-5-22

RGBval('rgb') is the same as RGBval(['r', 'g', 'b']) which is the same as RGBval([double('r'), double('g'), double('b')] which is the same as RGBval([114, 103, 98]). Characters, except for char(0), can be used as indices for arrays, and a vector of characters is transformed using double() to become a vector of indices.

There is no requirement that you use the minimum-memory data structure for operations if you have enough available memory.

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