topic Re: How to divide plot into smaller equal segment and find area under the curve? in SAS Enterprise Guide

How to divide plot into smaller equal segment and find area under the curve?

imanojkumar1 — Thu, 08 Dec 2016 08:01:46 GMT

For the following data, what I am trying to learn are:

1. plot and find area under the curve (which is calculated using either 1. Simpson's rule (https://en.wikipedia.org/wiki/Simpson%27s_rule) or, 2. Trapezoidal rule (https://en.wikipedia.org/wiki/Trapezoidal_rule) - Not sure if there are SAS's inbuilt functions for that.

2. Find the mid point on the plot, divide the plot into two 'A' and 'B' and then divide each of 'A' and 'B' in equal smaller segments (like black lines on the plot for section 'A' shown in the below pic, and calculate area for each segment (say Seg1 = xx mm2, Seg1 = xx1 mm2 and so forth)

data sample;
infile cards truncover expandtabs;
input X Y;
cards;
29 21
18 23
28 24
16 26
3 27
18 29
2 33
3 37
26 39
2 42
25 47
9 54
13 57
17 58
29 60
5 63
23 66
4 69
3 72
17 73
7 73
12 72
8 69
20 66
12 63
8 60
28 58
3 57
18 54
11 47
21 42
8 39
1 37
16 29
3 27
17 22
3 19
6 17
19 14
18 10
;
run;

I was trying something like this...

data Trapezoidal;
    set x_y end=last;
    retain integral;
    lag_x=lag(x); lag_y = lag(y);
    if _N_ eq 1 then integral = 0;
    else integral = integral + (x - lag_x) * (y + lag_y) / 2;
run;

Thanks.

Re: How to divide plot into smaller equal segment and find area under the curve?

Ksharp — Thu, 08 Dec 2016 11:45:48 GMT


data sample;
infile cards truncover expandtabs;
input X Y;
cards;
29 21
18 23
28 24
16 26
3 27
18 29
2 33
3 37
26 39
2 42
25 47
9 54
13 57
17 58
29 60
5 63
23 66
4 69
3 72
17 73
7 73
12 72
8 69
20 66
12 63
8 60
28 58
3 57
18 54
11 47
21 42
8 39
1 37
16 29
3 27
17 22
3 19
6 17
19 14
18 10
;
run;

proc sort data=sample ;
by x;
run;

proc sgplot data=sample;
needle x=x y=y;
run;

data Trapezoidal;
    set sample end=last;
    dif_x=dif(x); 
    mean_y=mean(lag(y),y);
    integral + (dif_x*mean_y);
    if last then putlog 'area under curve is ' integral;
run;

Re: How to divide plot into smaller equal segment and find area under the curve?

imanojkumar1 — Thu, 08 Dec 2016 12:46:34 GMT

Thanks for your help KSharp. I am just wondering why needle chart used and not line plot. Also, can we plot a vertical line (on X axis, at Y=MaxVal) in the middle of the plot.

Re: How to divide plot into smaller equal segment and find area under the curve?

Ksharp — Fri, 09 Dec 2016 04:46:12 GMT

Because that would be messed up .

Really suggest you post it at ODS Graphic forum.


data sample;
infile cards truncover expandtabs;
input X Y;
cards;
29 21
18 23
28 24
16 26
3 27
18 29
2 33
3 37
26 39
2 42
25 47
9 54
13 57
17 58
29 60
5 63
23 66
4 69
3 72
17 73
7 73
12 72
8 69
20 66
12 63
8 60
28 58
3 57
18 54
11 47
21 42
8 39
1 37
16 29
3 27
17 22
3 19
6 17
19 14
18 10
;
run;

proc sort data=sample ;
by x;
run;
proc sql;
select mean(x) into : x from sample ;
quit;
proc sgplot data=sample;
needle x=x y=y;
spline x=x y=y / lineattrs=graphdata4(thickness=4);
refline &x / axis=x lineattrs=(color=red thickness=4);
run;

data Trapezoidal;
    set sample end=last;
    dif_x=dif(x); 
    mean_y=mean(lag(y),y);
    integral + (dif_x*mean_y);
    if last then putlog 'area under curve is ' integral;
run;