Importing text file into Latex by character

Question

So I want to import a text file into latex character by character and format the individual characters by changing their color. So for instance, 'a' would be the color blue, 'b' would be red etc.

How should I go about importing the file? Should I make a database?

The input file is a simple text file extracted from fiction ebooks. I don't care much about the original formatting since the text file will be extracted from pdf or epub. So no equations and no special characters other than the one used in everyday english(. , ! ?).

So the input would probably be like:

"As an instance of what I mean, I remember meeting Monty Byng in Bond Street one morning, looking the last word in a grey check suit, and I felt I should never be happy till I had one like it."

Answer 1

For each letter used, let's say "x", there can be a corresponding macro \xxx with its color defined. This can be done with punctuation marks, for example exclamation points, via \expandafter\def\csname!!!\endcsname{...}.

The text is passed by way of macro \colorize.

EDITED for getting data from a file.

EDITED for using triple letters \lll as colorizing name, lest things like \ll confuse the algorithm.

EDITED so that non defined colorizing macros are presented in black.

Added an ADDENDUM (see bottom of this answer) to allow for an escape character to give primitive formatting ability within the \colorize macro argument.

The file sample.tex contains this data

cba def abc!

Here is my next pair of graphs!!!

Here is the file that reads and parses it.

\documentclass{article}
\usepackage{readarray}
\usepackage{xcolor}
\newcommand\colorize[1]{\expandafter\colorizepars#1\par\relax\relax}
\long\def\colorizepars#1\par#2\relax{%
  \ifx#1\relax\else
    \colorizewords#1 \relax\relax%
  \fi%
  \ifx\relax#2\else\par\colorizepars#2\relax\fi%
}
\def\colorizewords#1 #2\relax{%
  \ifx#1\relax\else
    \colorizeletters#1\relax\relax%
  \fi%
  \ifx\relax#2\else\ \colorizewords#2\relax\fi%
}
\makeatletter
\def\colorizeletters#1#2\relax{%
  \@ifundefined{#1#1#1}{#1}{\csname#1#1#1\endcsname}%
  \ifx\relax#2\else\colorizeletters#2\relax\fi}
\makeatother

\def\aaa{\textcolor{red}{a}}
\def\bbb{\textcolor{blue}{b}}
\def\ccc{\textcolor{green}{c}}
\def\ddd{\textcolor{cyan}{d}}
\def\eee{\textcolor{red!40}{e}}
\def\fff{\textcolor{blue!40}{f}}
\def\ggg{\textcolor{red!30!blue}{g}}
\def\hhh{\textcolor{green!40}{h}}
\def\nnn{\textcolor{yellow!40!green}{n}}
\def\ppp{\textcolor{orange}{p}}
\def\rrr{\textcolor{blue!30}{r}}
\def\ttt{\textcolor{green!40!blue}{t}}
\def\xxx{\textcolor{black!50}{x}}
\expandafter\def\csname!!!\endcsname{\textcolor{yellow}{!}}

\def\colorizeentry#1{\edef\tmp{\arrayij{mydata}{#1}{1}}\colorize{\tmp}}

\begin{document}
\colorize{%
abc def!

next paragraph Undefined letters are black.
}

Here is a way to get it from a file, if paragraphs are not needed

\readdef{sample.tex}{\x}
\colorize{\x}

If paragraphs are needed, you can place each paragraph in its own single row 
of the input file and parse line by line.

\copyrecords{mydata}% USES DATA FROM MOST RECENT \readdef; ASSIGNS ROWS TO "mydata"
\colorizeentry{1}

\colorizeentry{2}

\colorizeentry{3}
\end{document}

ZOOM IN

ZOOM OUT

---

ADDENDUM:

If you needed some primitive formatting ability in the colorized text, you could build in an escape character (here the [) as such:

\makeatletter
\def\colorizeletters#1#2#3\relax{%
  \ifx [#1\EscapeChar{#2}%
    \ifx\relax#3\else\colorizeletters#3\relax\fi%
  \else%
    \@ifundefined{#1#1#1}{#1}{\csname#1#1#1\endcsname}%
    \ifx\relax#2\else\colorizeletters#2#3\relax\relax\fi%
  \fi%
}
\makeatother
\def\EscapeChar#1{%
  \if 0#1\relax \textcolor{blue}{[}\else%
  \if 1#1\relax \bfseries\else%
  \if 2#1\relax \mdseries\else%
  \if 3#1\relax \itshape\else%
  \if 4#1\relax \upshape\else%
  \fi\fi\fi\fi\fi%
}

Then, the following code

\colorize{%
abc def!

next [1paragraph[2 [0Undefined] [3letters[4 are black.
}

would display as

Answer 2

With lualatex you could do something along the line of the chickenize package:

\documentclass{article}
\usepackage{fontspec,luacode}
\usepackage{luatexbase}
\begin{luacode}
 -- stolen from chickenize
 local nodenew = node.new
 local nodecopy = node.copy
 local nodetail = node.tail
 local nodeinsertbefore = node.insert_before
 local nodeinsertafter = node.insert_after
 local noderemove = node.remove
 local nodeid = node.id
 local nodetraverseid = node.traverse_id
 local nodeslide = node.slide

 Hhead = nodeid("hhead")
 RULE = nodeid("rule")
 GLUE = nodeid("glue")
 WHAT = nodeid("whatsit")
 COL = node.subtype("pdf_colorstack")
 GLYPH = nodeid("glyph")
 color_push = nodenew(WHAT,COL)
 color_pop = nodenew(WHAT,COL)
 color_push.stack = 0
 color_pop.stack = 0
 color_push.command = 1
 color_pop.command = 2


 mycolors={}
 mycolors[97]="1 0 0" --a
 mycolors[98]="0 1 0" --b
 mycolors[99]="0 0 1" --c
 mycolors[100]="0 1 1" --d

colortext = function(head)
  for line in nodetraverseid(0,head) do
    for i in nodetraverseid(37,line.head) do
        if mycolors[i.char] then     
        color_push.data = mycolors[i.char].." rg"  
        else 
        color_push.data = "0.5 0.5 0.5 rg"  -- gray for undefined
        end
        line.head = nodeinsertbefore(line.head,i,nodecopy(color_push))
        nodeinsertafter(line.head,i,nodecopy(color_pop))     
    end
  end
  return head
end

\end{luacode}

\def\colortext{
  \directlua{luatexbase.add_to_callback("post_linebreak_filter",colortext,"colortext")}}
\def\uncolortext{
  \directlua{luatexbase.remove_from_callback("post_linebreak_filter","colortext")}}

\newcommand\mytext{abcde}  
\begin{document}
\colortext abcdefgabc \section{abcxse}  \mytext

\uncolortext abcdefgabc
\end{document} 

Which gives something like this. (I don't know why the number of the section is black).

Answer 3

An expl3 version. The input (that can be from a file) is split into words and each word is split into letters that are colorized according to a table that can be easily augmented.

Limitations: only ASCII characters are allowed (unless you use XeLaTeX or LuaLaTeX and augment the table according to your wishes).

\begin{filecontents*}{filetocolorize.tex}
This file will be input.

Its words will be colorized.
\end{filecontents*}

\documentclass{article}
\usepackage{xparse}
\usepackage{xcolor}

\ExplSyntaxOn
\NewDocumentCommand{\colorize}{+m}
 {
  \codemonkey_colorize:n { #1 }
 }

\NewDocumentCommand{\colorizeinput}{m}
 {
  \tl_set_from_file:Nnn \l_codemonkey_colorize_input_tl { } { #1 }
  \codemonkey_colorize:V \l_codemonkey_colorize_input_tl
 }

\tl_new:N \l_codemonkey_colorize_input_tl
\seq_new:N \l_codemonkey_colorize_words_seq

\cs_new_protected:Npn \codemonkey_colorize:n #1
 {
  \seq_set_split:Nnn \l_codemonkey_colorize_words_seq { ~ } { #1 }
  \seq_map_inline:Nn \l_codemonkey_colorize_words_seq
   {
    \tl_map_inline:nn { ##1 } { \codemonkey_colorize_letter:n { ####1 } }
    \c_space_tl
   }
  \unskip % remove the last added space
 }

\cs_generate_variant:Nn \codemonkey_colorize:n { V }

\cs_new_protected:Npn \codemonkey_colorize_letter:n #1
 {
  \str_case:nnF { #1 }
   {
    {a}{\textcolor{red}{a}}
    {b}{\textcolor{blue}{b}}
    {c}{\textcolor{green}{c}}
    {d}{\textcolor{cyan}{d}}
    {e}{\textcolor{red!40}{e}}
    {f}{\textcolor{blue!40}{f}}
    {g}{\textcolor{red!30!blue}{g}}
    {h}{\textcolor{green!40}{h}}
    {n}{\textcolor{yellow!40!green}{n}}
    {p}{\textcolor{orange}{p}}
    {r}{\textcolor{blue!30}{r}}
    {t}{\textcolor{green!40!blue}{t}}
    {x}{\textcolor{black!50}{x}}
    {!}{\textcolor{yellow}{!}}
   }
   { % none of the above
    #1
   }
 }
\ExplSyntaxOff

\begin{document}

\colorize{abc def! 

next paragraph Undefined letters are black.}

Here is a way to get it from a file

\colorizeinput{filetocolorize}

\end{document}