Dictionaries
A dictionary is flexible data structure. Dictionaries:
- May optionally have an assigned text value.
- Hold a flexible set of key-value pairs. Keys are text names.
- Information is automatically sorted by key, resulting in fast searching and retrieval.
- Key-value pairs can be added and removed efficiently and without limit.
- Values may be other dictionaries, allowing you to create complex data structures.
Create a Dictionary Using the Dictionary() Function
In this example ServerLocations is a dictionary of server names and where each is located.
ServerLocations = Dictionary();
ServerLocations["Primary"] = "Cleveland";
ServerLocations["Backup1"] = "Orlando";
In the following example, DriverServers is a dictionary of dictionaries, each holding the names of primary and packup servers.
DriverServers = Dictionary(); DriverServers["Modicon1"] = Dictionary(); DriverServers["Modicon1"]["Primary"] = "ServerX"; DriverServers["Modicon1"]["Backup"] = "ServerY"; DriverServers["Modicon2"] = Dictionary(); DriverServers["Modicon2"]["Primary"] = "ServerY"; DriverServers["Modicon2"]["Backup"] = "ServerX";
Within a dictionary, all keys must always be unique by definition. Attempting to create a duplicate key by assigning a new value to a key with a non-unique name will simply result in the original key being assigned the new data value. Dictionaries may be defined such that their keys are case sensitive (in which case "a" will come after "Z") or they may be non case sensitive. Unless otherwise specified, they will not be case sensitive.
Practice with dictionaries
Arrays are useful for storing data in a clearly enumerated order, 0, 1, 2... But often, data is associated with keys that aren't in a tidy order. There are cases where driver error codes provide an excellent example of this.
In this example, you will use an array and listbox to simulate random error codes coming from hardware. A dictionary stores the key-value pairs of defined error codes and matching messages.
Create a new script application and copy the following to the Graphics submodule.
Graphics
[
ErrCodes { a dictionary of error codes };
SimErrors { array simulating errors received };
Choice { selection from simulated error array };
Index { offset into array };
Msg { message to display };
]
Init [
If 1 Main;
[
ErrCodes = Dictionary(1);
ErrCodes[0x2] = "No connection";
ErrCodes[0x4] = "Missing adapter";
ErrCodes[0x10] = "Error retrieving value";
ErrCodes[0x30] = "Command not found";
ErrCodes[0x92] = "Invalid syntax";
SimErrors = New(5);
SimErrors[0] = 0x2;
SimErrors[1] = 0x4;
SimErrors[2] = 0x10;
SimErrors[3] = 0x30;
SimErrors[4] = 0x92;
]
]
Main [
System.DropList(40, 60, 140, 40 { Boundaries of list },
SimErrors { Data displayed },
"" { No title },
Index { Highlighted index },
1, 1 { Focus ID, trigger },
FALSE { Editable field },
Invalid { Starting value },
Choice { Variable to set },
FALSE { No bevel },
0 { Align top of list });
Msg = Concat("Error code: ", Choice, " ... Message: ", ErrCodes[Choice]);
ZText(150, 60, Msg, 12, 0);
]
{ End of System\Graphics }
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