Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

R: Explained differences of max, maximum , sum, etc. #6732

Merged
merged 2 commits into from
May 3, 2014
Merged

R: Explained differences of max, maximum , sum, etc. #6732

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
740ece2
R: Explained differences of max, maximum , sum, etc.
mkriele May 3, 2014
1099474
changed colletion to collection
mkriele May 3, 2014
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 2 additions & 0 deletions doc/manual/noteworthy-differences.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,8 @@ One of Julia's goals is to provide an effective language for data analysis and s
- In Julia, values are passed and assigned by reference. If a function modifies an array, the changes will be visible in the caller. This is very different from R and allows new functions to operate on large data structures much more efficiently.
- Concatenation of vectors and matrices is done using ``hcat`` and ``vcat``, not ``c``, ``rbind`` and ``cbind``.
- A Julia range object like ``a:b`` is not shorthand for a vector like in R, but is a specialized type of object that is used for iteration without high memory overhead. To convert a range into a vector, you need to wrap the range with brackets ``[a:b]``.
- ``max``, ``min`` are the equivalent of ``pmax`` and ``pmin`` in R, but both arguments need to have the same dimensions. While ``maximum``, ``minimum`` replace ``max`` and ``min`` in R, there are important differences.
- The functions ``sum``, ``prod``, ``maximum``, ``minimum`` are different from their counterparts in R. They all accept one or two arguments. The first argument is an iterable collection such as an array. If there is a second argument, then this argument indicates the dimensions, over which the operation is carried out. For instance, let ``A=[[1 2],[3,4]]`` in Julia and ``B=rbind(c(1,2),c(3,4))`` be the same matrix in R. Then ``sum(A)`` gives the same result as ``sum(B)``, but ``sum(A,1)`` is a row vector containing the sum over each column and ``sum(A,2)`` is a column vector containing the sum over each row. This contrasts to the behavior of R, where ``sum(B,1)=11`` and ``sum(B,2)=12``. If the second argument is a vector, then it specifies all the dimensions over which the sum is performed, e.g., ``sum(A,[1,2])=10``. It should be noted that there is no error checking regarding the second argument.
- Julia has several functions that can mutate their arguments. For example, it has ``sort(v)`` and ``sort!(v)``.
- ``colMeans()`` and ``rowMeans()``, ``size(m, 1)`` and ``size(m, 2)``
- In R, performance requires vectorization. In Julia, almost the opposite is true: the best performing code is often achieved by using devectorized loops.
Expand Down