CODEWITHSUNDEEP
c++booststd
ast4
ast4

Reputation: 791

C++ efficiently extracting subsets from vector of user defined structure

Let me preface this with the statement that most of my background has been with functional programming languages so I'm fairly novice with C++.

Anyhow, the problem I'm working on is that I'm parsing a csv file with multiple variable types. A sample line from the data looks as such:

"2011-04-14 16:00:00, X, 1314.52, P, 812.1, 812"
"2011-04-14 16:01:00, X, 1316.32, P, 813.2, 813.1"
"2011-04-14 16:02:00, X, 1315.23, C, 811.2, 811.1"

So what I've done is defined a struct which stores each line. Then each of these are stored in a std::vector< mystruct >. Now say I want to subset this vector by column 4 into two vectors where every element with P in it is in one and C in the other.

Now the example I gave is fairly simplified, but the actual problem involves subsetting multiple times.

My initial naive implementation was iterate through the entire vector, creating individual subsets defined by new vectors, then subsetting those newly created vectors. Maybe something a bit more memory efficient would be to create an index, which would then be shrunk down.

Now my question is, is there a more efficient, in terms of speed/memory usage) way to do this either by this std::vector< mystruct > framework or if there's some better data structure to handle this type of thing.

Thanks!

EDIT:

Basically the output I'd like is first two lines and last line separately. Another thing worth noting, is that typically the dataset is not ordered like the example, so the Cs and Ps are not grouped together.

Upvotes: 2

Views: 697

Answers (3)

Gabriel Schreiber
Gabriel Schreiber

Reputation: 2226

I understand you have not per se trouble doing this but you seem to be concerned about memory usage and performance.

Depending on the size of your struct and the number of entries in the csv file it may be advisabe to use a smart pointer if you don't need to modify the partitioned data so the mystruct objects are not copied:

typedef std::vector<boost::shared_ptr<mystruct> > table_t;
table_t cvs_data;

If you use std::partition (as another poster suggested) you need to define a predicate that takes the indirection of the shared_ptr into accont.

Upvotes: 0

Akobold
Akobold

Reputation: 946

If you want a data structure that allows you to move elements between different instances cheaply, the data structure you are looking for is std::list<> and it's splice() family of functions.

Upvotes: 0

Jay
Jay

Reputation: 14471

I've used std::partition for this. It's not part of boost though.

Upvotes: 1

Related Questions