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Tips and tricks: Difference between revisions
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inds = isnan(A); | inds = isnan(A); | ||
B(!inds) = num2cell(A(!inds)) | B(!inds) = num2cell(A(!inds)) | ||
This gets you a 1 column cell array. You can reshape it to the original size by using the <code>reshape</function> | This gets you a 1 column cell array. You can reshape it to the original size by using the <code>reshape</function> | ||
The next version of octave (3.6) implements the <code>CollectOutput</code> switch as seen in example 8 here: http://www.mathworks.com/help/techdoc/ref/textscan.html | The next version of octave (3.6) implements the <code>CollectOutput</code> switch as seen in example 8 here: http://www.mathworks.com/help/techdoc/ref/textscan.html | ||
==Using Variable Strings in Octave Commands== | |||
For example, to plot data using a string variable as a legend: | |||
Option 1 (simplest): | |||
legend = "-1;My data;"; | |||
plot(x, y, legend); | |||
Option 2 (to insert variables): | |||
plot(x, y, sprintf("-1;%s;", dataName)); | |||
Option 3 (not as neat): | |||
legend = 'my legend'; | |||
plot_command = ['plot(x,y,\';',legend,';\')']; | |||
eval(plot_command); | |||
These same tricks are useful for reading and writing data files with unique names, etc. | |||
==Vectorizing Tricks=== | |||
You can easily fill a vector with an index: | |||
for i=1:n, x(i) = i; end | |||
x = [1:n]; | |||
This works for expressions on the index by wrapping the index in an expression: | |||
for i=1:n, x(i) = sin(2*pi*i*f/r); end | |||
x = sin(2*pi*[1:n]*f/r); | |||
You can also work with other vectors this way: | |||
for i=1:n, x(i) = sin(2*pi*y(i)*f/r); end | |||
x = sin(2*pi*y*f/r); | |||
Conditionals in the for loop are a little bit tricky. We need to create an index vector for the true condition, and another for the false condition, then calculate the two independently. | |||
for i=1:n, if y(i)<1, x(i)=y(i); else x(i) = 2*y(i); endif | |||
idx = y < 1; | |||
x(idx) = y(idx); | |||
x(!idx) = 2*y(!idx); | |||
FIXME: add the following | |||
*examples from matrices | |||
*tricks with sort and cumsum (e.g., hist, lookup) | |||
*counter-examples such as a tridiagonal solver | |||
*sparse matrix tricks | |||
*tricks relying on fortran indexing | |||
===Other references=== | |||
*MATLAB array manipulation tips and tricks by Peter Acklam: http://home.online.no/~pjacklam/matlab/doc/mtt/index.html | |||
*The MathWorks: Code Vectorization Guide: http://www.mathworks.com/support/tech-notes/1100/1109.html | |||