PredatorPrey_step11

11. Writing Files

This 11th step illustrates how to save data in a text file.

Formulation

• At each simulation step, write in a text file:
  • The time step
  • The number of prey and predator agents
  • The min and max energy of the prey and predator agents

Model Definition

global section

The main way to write data inside a file is to use the save statement:

save my_data type: file_type to: file_name;

With:

• my_data: depends on the data to save and of the type of file
• file_type : string
• file_name : string

There are 3 main possible types:

• shp (shapefile - GIS data): in that case, my_data is treated as a list of agents or geometries: all their geometries are saved in the file (with some variables as attributes),
• txt (text): in that case, my_data is treated as a string, which is written directly in the file,
• csv: in that case, my_data is treated as a list of values: [val1, val2, val3], that will be written in the file, separated by the , separator.

We use this statement (in a global reflex called save_result) to write:

• The cycle step: use of the cycle keyword that returns the current simulation step.
• The number of prey and predator agents: use of nb_preys and nb_predators variables.
• The min and max energy of the prey and predator agents: use of list min_of expression and list max_of expression keywords.

reflex save_result when: (nb_preys > 0) and (nb_predators > 0){
    save ("cycle: "+ cycle + "; nbPreys: " + nb_preys
	  + "; minEnergyPreys: " + (prey min_of each.energy)
	  + "; maxSizePreys: " + (prey max_of each.energy) 
	  + "; nbPredators: " + nb_predators           
	  + "; minEnergyPredators: " + (predator min_of each.energy)          
	  + "; maxSizePredators: " + (predator max_of each.energy)) 
	  to: "results.txt" type: "text" rewrite: (cycle = 0) ? true : false;
}

Complete Model

https://github.com/gama-platform/gama/blob/GAMA_1.9.2/msi.gama.models/models/Tutorials/Predator%20Prey/models/Model%2011.gaml