Using a data file as input in tikz

Question

I have a sorted data in a file (named data.dat). These data should be plotted vertically. I prepared a code in latex using tikz that works. The problem is each data is typed one by one in the main body of the code and I need a way in which I call the data file and each data is substituted one by one. Here is my code

\documentclass[border= 5 pt]{standalone} 
\usepackage{times,comment}
\usepackage{graphicx}
\usepackage{tikz}


\newcommand{\point}[1]{
\draw [<->,purple] ( 0 , #1 ) node[yshift=0,left,font=\tiny]{  #1 }  -- ( 1 , #1 ) node[yshift=0,right,font=\tiny]{  #1 } ; }

\begin{document}

\begin{tikzpicture}[scale=1]
\point{0}    
\point{1}
\point{2}
\point{2.5}    
\point{3.4}
\point{4}
\point{5.8}
\point{6.9}
\point{7.5}

\end{tikzpicture}

\end{document}

The data file can be download from here.

Answer 1

As pointed out by Henri Menke, you could use pgfplots to plot the data. Assuming you want to use TikZ and your command \point instead, you could use pgfplotstable to load and loop over the data. (You won't need \begin{filecontents*}{data.dat} ... \end{filecontents*} because you already have data.dat, this is just to make it more convenient for others to get the file on their system.)

\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{filecontents}
\begin{filecontents*}{data.dat}
0
1
2
2.5
3.4
4
5.8
6.9
7.5
\end{filecontents*}
\usepackage{pgfplotstable}
\pgfplotsset{compat=1.16}
% from https://tex.stackexchange.com/a/445369/121799
\newcommand*{\ReadOutElement}[4]{%
    \pgfplotstablegetelem{#2}{#3}\of{#1}%
    \let#4\pgfplotsretval
}
\newcommand{\point}[1]{
\draw [<->,purple] ( 0 , #1 ) node[yshift=0,left,font=\tiny]{  #1 }  -- ( 1 , #1 ) node[yshift=0,right,font=\tiny]{  #1 } ; }

\begin{document}

\begin{tikzpicture}[scale=1]
\pgfplotstableread[header=false]{data.dat}\datatable
\pgfplotstablegetrowsof{\datatable}
\pgfmathtruncatemacro{\rownum}{\pgfplotsretval-1}
\foreach \X in {0,...,\rownum}
{\ReadOutElement{\datatable}{\X}{[index]0}{\tmpx}
\point{\tmpx}
}
\end{tikzpicture}

\end{document}

Answer 2

Although in this case you can use pgfplots lo load the external data (+1) and in other type of macros probably you can also use the datatool package, in case you know R and knitr, here are another approach to access individual values as argument of a macro: load the external data as an R data frame object, said with name "data", and then access concrete values of this vector as \Sexpr{data[3,1]} (print the third value of first column).

To load the external CSV file as a data.frame, you can use the read.csv() R function but for the example I created the data frame from the scratch:

\documentclass{article} 
\usepackage{times,comment}
\usepackage{graphicx}
\usepackage{tikz}
\newcommand{\point}[1]{
\draw [<->,purple] ( 0 , #1 ) node[yshift=0,left,
font=\tiny]{  #1 }  -- ( 1 , #1 ) node[yshift=0,right,font=\tiny]{  #1 } ; }
\begin{document}
<<mydata,echo=F>>=
# data <- read.csv("data.dat", sep=",", header=F) # to load external data
data <- data.frame(x=c(0,1,2,2.5,3.4,4,5.8,6.9,7.5)) # internal data
@
\begin{tikzpicture}[scale=1]
\point{\Sexpr{data[1,1]}}    
\point{\Sexpr{data[2,1]}}    
\point{\Sexpr{data[3,1]}}    
\point{\Sexpr{data[4,1]}}    
\point{\Sexpr{data[5,1]}}    
\point{\Sexpr{data[6,1]}}    
\point{\Sexpr{data[7,1]}}    
\point{\Sexpr{data[8,1]}}    
\point{\Sexpr{data[9,1]}}    
\end{tikzpicture}
\end{document}

(The result is identical to the image of marmot, no need to add it twice).