August 8–10. Iowa State University, Ames, Iowa
You can use any resource on the web, apart from asking people questions (no asking on R help!)
Email your answers, as a single text file, to email@example.com. You are encouraged to submit answers as you complete them - and they may be revised with a final update at the end.
Each of the three tasks will be graded as follows:
Bonus points will be awarded for particularly elegant/concise/generalisable/well documented solutions.
Ties will be broken by submission time.
My client has recorded her observations as m1, m2, ..., m10, f1, ..., f10.
obs <- c("f7", "f8", "m1", "m2", "m3", "f3", "m4", "f1", "m7", "m7", "f4", "m5", "f5", "m6", "f6", "m8", "m9", "f9", "m10", "f10", "f2")
Actually, she should have recorded them as two variables. The first should be an integer variable corresponding to the integer portion of her observations, and the second should be a categorical variable with the two levels "male" and "female".
Your answer should be in the form of a function which takes the vector above and returns a data frame with two columns.
You have data with multiple observations per person and need to perform the following tasks
An example data frame 'ragged' is in 'ragged.rda' (rename to rda after downloading).
The data set has multiple observations per person, with people identified by values the 'id' variable.
'visittime' is the time that the observation was made. Everyone has an observation at time 0.
'futime' is the end of follow-up for the person. Suitable variables for part 3 include '
visittime'. For part 4, suitable variables include '
(a) Many binary operators in R have 'reducing' or 'folding' versions that collapse a vector to a single number
"+" sum() 1+2+3+4 == sum(c(1,2,3,4)) "*" prod() 1*2*3*4 == prod(c(1,2,3,4)) "&" all() a & b & c == all(c(a, b, c)) "|" any() a | b | c == any(c(a, b, c))
Write a function
reduce(x, operator) that generalizes this process to an arbitrary binary operator, so that
reduce(x,"+") would be the same as
(b) The binary operators "+" and "*" have cumulative versions
cumprod() so that
cumsum(c(1,2,3,4)) = c(1, 1+2, 1+2+3, 1+2+3+4) cumprod(c(1,2,3,4)) = c(1, 1*2, 1*2*3, 1*2*3*4)
Write a function
accumulate(x, operator) that generalizes this to an arbitrary binary operator, so that
accumulate(x, "+") would be the same as