{"id":5140,"date":"2013-09-25T11:13:35","date_gmt":"2013-09-25T10:13:35","guid":{"rendered":"http:\/\/www.walkingrandomly.com\/?p=5140"},"modified":"2014-02-26T10:24:34","modified_gmt":"2014-02-26T09:24:34","slug":"lamenting-the-lack-of-multiple-assignment-in-matlab","status":"publish","type":"post","link":"https:\/\/walkingrandomly.com\/?p=5140","title":{"rendered":"Lamenting the lack of multiple assignment in MATLAB"},"content":{"rendered":"

I support scientific applications at The University of Manchester<\/a> (see my LinkedIn profile<\/a> if you’re interested in the details) and part of my job involves working on code written by researchers in a variety of languages. \u00a0When I say ‘variety’ I really mean it – MATLAB, Mathematica, Python, C, Fortran, Julia, Maple, Visual Basic and PowerShell are some languages I’ve worked with this month for instance.<\/p>\n

Having to juggle the semantics of so many languages in my head sometimes leads to momentary confusion when working on someone’s program. \u00a0For example, I’ve been doing a lot of Python work recently but this morning I was hacking away on someone’s MATLAB code. \u00a0Buried deep within the program, it would have been very sensible to be able to do the equivalent of this:<\/p>\n

a=rand(3,3)\r\n\r\na =\r\n    0.8147    0.9134    0.2785\r\n    0.9058    0.6324    0.5469\r\n    0.1270    0.0975    0.9575\r\n\r\n>> [x,y,z]=a(:,1)\r\n\r\nIndexing cannot yield multiple results.<\/pre>\n
That is, I want to be able to take the first column of the matrix a and broadcast it out to the variables x,y and z. The code I’m working on uses MUCH bigger matrices and this kind of assignment is occasionally useful since the variable names x,y,z have slightly more meaning than a(1,3), a(2,3), a(3,3).<\/p>\n
The only concise way I’ve been able to do something like this using native MATLAB commands is to first convert to a cell. In MATLAB 2013a for instance:<\/p>\n
>> temp=num2cell(a(:,1));\r\n>> [x y z] = temp{:}\r\n\r\nx =\r\n    0.8147\r\n\r\ny =\r\n    0.9058\r\n\r\nz =\r\n    0.1270<\/pre>\n
This works but I think it looks ugly and introduces conversion overheads. The problem I had for a short time is that I subconsciously expected multiple assignment to ‘Just Work’ in MATLAB since the concept makes sense in several other languages I use regularly.<\/p>\n
Python<\/a>:<\/p>\n
from pylab import rand\r\na=rand(3,3)\r\n[a,b,c]=a[:,0]<\/pre>\n
Mathematica<\/a>:<\/p>\n
a = RandomReal[1, {3, 3}]\r\n{x,y,z}=a[[All,1]]<\/pre>\n
Julia<\/a>:<\/p>\n
a=rand(3,3);\r\n(x,y,z)=a[:,1]<\/pre>\n
I’ll admit that I don’t often need this construct in MATLAB but it would definitely be occasionally useful. I wonder what other opinions there are out there? Do you think multiple assignment is useful (in any language)?<\/p>\n","protected":false},"excerpt":{"rendered":"
I support scientific applications at The University of Manchester (see my LinkedIn profile if you’re interested in the details) and part of my job involves working on code written by researchers in a variety of languages. \u00a0When I say ‘variety’ I really mean it – MATLAB, Mathematica, Python, C, Fortran, Julia, Maple, Visual Basic and […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[59,8,11,7,31],"tags":[],"class_list":["post-5140","post","type-post","status-publish","format-standard","hentry","category-julia","category-mathematica","category-matlab","category-programming","category-python"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p3swhs-1kU","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts\/5140","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5140"}],"version-history":[{"count":5,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts\/5140\/revisions"}],"predecessor-version":[{"id":5378,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=\/wp\/v2\/posts\/5140\/revisions\/5378"}],"wp:attachment":[{"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5140"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5140"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/walkingrandomly.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5140"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}