dhruva escribió:

Hi, I have a struct with 2 members as follows:

typedef struct time_series { time_t _time; double _value; } time_series_t;

The data I get is sorted by time as it is a time series. I would like to maintain another index sorted by value. Since I need to keep removing the oldest records, I need the time based order and since I need to compute percentile, I need to sort it based on value. Would using multi-index save space (and time in insertion and removal) compared to having 2 vectors with different sort order?

The space taken per element by the Boost.MultiIndex-based solution would be: 6p+sizeof(time_series_t) where p is the size of a pointer, 4 bytes in a typical 32-bit architecture. (See http://www.boost.org/libs/multi_index/doc/performance.html for details.) As for having two vectors, one with the time_series_t objects themselves, the second with pointers to the elements of the first one, the space per element is c(p+sizeof(time_series_t)) where c is the capacity() to size() ratio for the vectors, which oscillates (unless explicitly controlled by the user) between 1 and some lib-specific upper bound (2 or 1.5 in most cases). So, if we have for instance p=4, sizeof(time_series_t)=16, c=1.25 that would yield 40 bytes per element for scenario 1 and 25 bytes per element for scenario 2. Your mileage may vary depending on your particular environment. As for speed, this much depends on your usage patterns: how often you sort the vectors, prune them, etc. In particular, take into account that removing elements from a position in a vector other than the tail is expensive, which might lead you to use (the more space-consuming) std::queues instead. I guess your best option is to prototype both scenarios and profile them. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo