Date: Jun 16, 2013 5:10 AM
Author: David Park
Subject: Re: Getting the plotted data from a graph
Lily,

You should be aware that the points that you obtain are dependent upon the

details of the plotting algorithm. Here I have used Options simply to limit

the number of points.

g1 = Plot[Sin[x], {x, -Pi, Pi}, PlotPoints -> 20, MaxRecursion -> 1,

Frame -> True, FrameLabel -> {"x", "y"}, ImageSize -> 2.6*72]

If you keep clicking on the plotted line Mathematica will display the points

it used to draw the curve. However, that does not get their coordinates. You

could extract their coordinates using:

First@Cases[First[g1], ln_Line :> First[ln], Infinity]

{{-3.14159, -3.30694*10^-7}, {-2.98256, -0.158362}, {-2.82353, \

-0.312727}, {-2.65112, -0.471041}, {-2.47871, -0.615389}, {-2.31773, \

-0.733775}, {-2.15675, -0.833186}, {-1.99892, -0.909745}, {-1.8411, \

-0.963691}, {-1.6699, -0.995094}, {-1.49869, -0.997402}, {-1.33892, \

-0.973236}, {-1.17914, -0.924278}, {-1.00599, -0.84469}, {-0.832833, \

-0.73984}, {-0.662837, -0.615356}, {-0.492841, -0.473131}, \

{-0.334271, -0.32808}, {-0.1757, -0.174797}, {0.168195,

0.167403}, {0.489239, 0.469954}, {0.646604, 0.602479}, {0.803968,

0.720115}, {0.974709, 0.827539}, {1.14545, 0.910896}, {1.30477,

0.964822}, {1.46408, 0.994311}, {1.63678, 0.997824}, {1.80947,

0.971653}, {1.979, 0.917834}, {2.14854, 0.837698}, {2.30665,

0.741259}, {2.46476, 0.626329}, {2.63624, 0.484112}, {2.80773,

0.327694}, {2.97466, 0.166157}, {3.14159, 3.30694*10^-7}}

The Presentations Application has a command that makes this a bit more

convenient.

<< Presentations `

Extract2DLinePoints[g1]

So you could draw the curve and then plot the points used on top of it.

Draw2D[

{g1 = Draw[Sin[x], {x, -Pi, Pi}, PlotPoints -> 20, MaxRecursion -> 1],

PointSize[0.015],

Point /@ Extract2DLinePoints[g1]},

Frame -> True, FrameLabel -> {"x", "y"}]

David Park

djmpark@comcast.net

http://home.comcast.net/~djmpark/index.html

From: Lily T. [mailto:econactually@gmail.com]

Dear All,

My question is regarding the plotted data points in a graph. Assume you draw

a graph of sinx as:

g1 = Plot[Sin[x], {x, -Pi, Pi},

Frame -> True, FrameLabel -> {"x", "y"}, ImageSize -> 2.6*72

]

then how can I get all of the data points of this graph by using

mathematica?

This is really important for me and I couldn't find the answer anywhere

online!

Thank you for your help in advance!

Best,

Lily