Skip to main content

programming - Reading from STDIN, or: how to pipe data into Mathematica


Today I tried using Mathematica's plotting capabilities to display the output of a C++ program. This made me wonder whether it is possible to somehow tell a Mathematica script to read from STDIN and then do something with that, a la


#/usr/local/bin/MathematicaScript -script

(* Mathematica plotting script *)
data = ReadStream["STDIN"];
plot = ListPlot[data];
Export[plot, ...];


which can then be used like


./cppDataGenerator | mathematicaPlotScript

However, I couldn't find much on that in the documentation, the entries always focus on output or string streams, and trial and error didn't yield a result either.


So the question is: How can I make a Mathematica script listen on the standard input?



Answer



Extending on nixeagle's answer, here's what I've come up with.


First of all, the thing I overlooked is the 3rd/5th bullet point when clicking More Information in the help for Input/InputString, it could not be hidden any better:



When no front end is used, Input reads from standard input.




Well that answers that, the rest was finding out how these two functions work. To my knowledge, their difference is that InputString reads STDIN like any other language, while Input interprets STDIN as Mathematica input directly; therefore, I assume that, for practical purposes, Input[] == ToExpression[InputString[]].


So let's try that out:


#!/usr/local/bin/MathematicaScript -script
Print@Input[];


> echo "2^10" | ./mscript
1024


Now back to my plotting problem, there is still an issue: Input seems to stop reading when it encounters a new line, which is of course not desired when giving a large file to the script; I'd much rather have it stop at the EOF byte. However, I wasn't able to find a setting that changes this behavior.


Comments

Popular posts from this blog

plotting - How to draw lines between specified dots on ListPlot?

I would like to create a plot where I have unconnected dots and some connected. So far, I have figured out how to draw the dots. My code is the following: ListPlot[{{1, 1}, {2, 2}, {3, 3}, {4, 4}, {1, 4}, {2, 5}, {3, 6}, {4, 7}, {1, 7}, {2, 8}, {3, 9}, {4, 10}, {1, 10}, {2, 11}, {3, 12}, {4,13}, {2.5, 7}}, Ticks -> {{1, 2, 3, 4}, None}, AxesStyle -> Thin, TicksStyle -> Directive[Black, Bold, 12], Mesh -> Full] I have thought using ListLinePlot command, but I don't know how to specify to the command to draw only selected lines between the dots. Do have any suggestions/hints on how to do that? Thank you. Answer One possibility would be to use Epilog with Line : ListPlot[ {{1, 1}, {2, 2}, {3, 3}, {4, 4}, {1, 4}, {2, 5}, {3, 6}, {4, 7}, {1, 7}, {2, 8}, {3, 9}, {4, 10}, {1, 10}, {2, 11}, {3, 12}, {4, 13}, {2.5, 7}}, Ticks -> {{1, 2, 3, 4}, None}, AxesStyle -> Thin, TicksStyle -> Directive[Black, Bold, 12], Mesh -> Full, Epilog -> { Line[ ...

equation solving - Invert and fit implicitly defined curve

I need to fit an implicitly defined curve. I thought I could get some data out of Solve , and then using FindFit . Therefore, I would like to find the relation the parametric curve defined by $F(x,y)=0$: Solve[-(1/2) + 1/2 (0.41202 BesselK[0, 0.1 Sqrt[x^2 + y^2]] + (0.101483 x BesselK[1, 0.1 Sqrt[x^2 + y^2]])/Sqrt[x^2 + y^2]) == 0, y] But I can't get an output: Solve was unable to solve the system with inexact coefficients or the system obtained by direct rationalization of inexact numbers present in the system. Since many of the methods used by Solve require exact input, providing Solve with an exact version of the system may help. >> Edit: In particular, I would like to fit the data coming from the curve with the expression of another curve, and not with a function $f(x)$. In particular, since this clearly looks like a cardioid , I would like it to fit to something like it. What other strategies could I try?

dynamic - How can I make a clickable ArrayPlot that returns input?

I would like to create a dynamic ArrayPlot so that the rectangles, when clicked, provide the input. Can I use ArrayPlot for this? Or is there something else I should have to use? Answer ArrayPlot is much more than just a simple array like Grid : it represents a ranged 2D dataset, and its visualization can be finetuned by options like DataReversed and DataRange . These features make it quite complicated to reproduce the same layout and order with Grid . Here I offer AnnotatedArrayPlot which comes in handy when your dataset is more than just a flat 2D array. The dynamic interface allows highlighting individual cells and possibly interacting with them. AnnotatedArrayPlot works the same way as ArrayPlot and accepts the same options plus Enabled , HighlightCoordinates , HighlightStyle and HighlightElementFunction . data = {{Missing["HasSomeMoreData"], GrayLevel[ 1], {RGBColor[0, 1, 1], RGBColor[0, 0, 1], GrayLevel[1]}, RGBColor[0, 1, 0]}, {GrayLevel[0], GrayLevel...