Archive for R exam

Buffon needled R exams

Posted in Books, Kids, R, Statistics, University life with tags , , , , , , , on November 25, 2013 by xi'an

Here are two exercises I wrote for my R mid-term exam in Paris-Dauphine around Buffon’s needle problem. In the end, the problems sounded too long and too hard for my 3rd year students so I opted for softer questions. So recycle those if you wish (but do not ask for solutions!)

R finals

Posted in R, Statistics, University life with tags , , , , , , , , on January 31, 2013 by xi'an

From my office in Dauphine, on the hottest day of the year (so far)...On the morning I returned from Varanasi and the ISBA meeting there, I had to give my R final exam (along with three of my colleagues in Paris-Dauphine). This year, the R course was completely in English, exam included, which means I can post it here as it may attract more interest than the French examens of past years…

I just completed grading my 32 copies, all from exam A, which takes a while as I have to check (and sometimes recover) the R code, and often to correct the obvious mistakes to see if the deeper understanding of the concepts is there. This year student cohort is surprisingly homogeneous: I did not spot any of the horrors I may have mentioned in previous posts.

I must alas acknowledge a grievous typo in the version of Exam B that was used the day of the final: cutting-and-pasting from A to B, I forgot to change the parameters in Exercise 2, asking them to simulate a Gamma(0,1). It is only after half an hour that a bright student pointed out the impossibility… We had tested the exams prior to printing them but this somehow escaped the four of us!

Now, as I was entering my grades into the global spreadsheet, I noticed a perfect… lack of correlation between those and the grades at the midterm exam. I wonder what that means: I could be grading at random, the levels in November and in January could be uncorrelated, some students could have cheated in November and others in January, student’s names or file names got mixed up, …? A rather surprising outcome!

grades of some of my students at the midterm and finals R exams

R midterms

Posted in Kids, Linux, R, Statistics, University life with tags , , , , , , , , , , , on November 9, 2012 by xi'an

Here are my R midterm exams, version A and version B in English (as students are sitting next to one another in the computer rooms), on simulation methods for my undergrad exploratory statistics course. Nothing particularly exciting or innovative! Dedicated ‘Og‘s readers may spot a few Le Monde puzzles in the lot…

Two rather entertaining if mundane occurences related to this R exam: one hour prior to the exam, a student came to my office to beg for being allowed to take the solution manual with her (as those midterm exercises are actually picked from an exercise booklet, some students cooperated towards producing a complete solution manual and this within a week!), kind of missing the main point of having an exam. (I have not seen yet this manual but I’d be quite interested in checking the code they produced on that occasion…) During the exam, another student asked me what was the R command to turn any density into a random generator: he had written a density function called mydens and could not fathom why rmydens(n) was not working. The same student later called me as his computer was “stuck”: he was not aware that a “+” prompt on the command line meant R was waiting for him to complete the command… A less comical event that ended well is that a student failed to save her R code (periodically and) at the end of the exam and we had to dig very deep into the machine to salvage her R commands from \tmp as rkward safeguards, as only the .RData file was available at first. I am glad we found this before turning the machine off, otherwise it would have been lost.

back from down under

Posted in Books, pictures, R, Statistics, Travel, University life with tags , , , , , , , , , , , , , , on August 30, 2012 by xi'an

After a sunny weekend to unpack and unwind, I am now back to my normal schedule, on my way to Paris-Dauphine for an R (second-chance) exam. Except for confusing my turn signal for my wiper, thanks to two weeks of intensive driving in four Australian states!, things are thus back to “normal”, meaning that I have enough of a control of my time to handle both daily chores like the R exam and long-term projects. Including the special issues of Statistical Science, TOMACS, and CHANCE (reviewing all books of George Casella in memoriam). And the organisation of MCMSki 4, definitely taking place in Chamonix on January 6-8, 2014, hopefully under the sponsorship of the newly created BayesComp section of ISBA. And enough broadband to check my usual sites and to blog ad nauseam.

This trip to Australia, along the AMSI Lectures as well as the longer visits to Monash and QUT, has been quite an exciting time, with many people met and ideas discussed. I came back with a (highly positive) impression of Australian universities as very active places, just along my impression of Australia being a very dynamic and thriving country, far far away from the European recession. I was particularly impressed by the number of students within Kerrie Mengersen’s BRAG group, when we did held discussions in classrooms that felt full like a regular undergrad class! Those discussions and meetings set me towards a few new projects along the themes of mixture estimation and model choice, as well as convergence assessment. During this trip, I however also felt the lack of long “free times” I have gotten used to, thanks to the IUF chair support, where I can pursue a given problem for a few hours without interruption. Which means that I did not work as much as I wanted to during this tour and will certainly avoid such multiple-step trips in a near future. Nonetheless, overall, the own under” experience was quite worth it! (Even without considering the two weeks of vacations I squeezed in the middle.)

Back to “normal” also means I already had two long delays caused by suicides on my train line…


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