This subflow helps to store timeseries information in a local file (inside the hard disk or the uSD card) following the CSV (comma-separeted values) format. It is very useful when you want to track some variables that evolve over time, saving the values in a .csv file and analyzing the data later in a spreadsheet (Libreoffice Calc, Google Spreadsheet or Microsoft Excel). The subflow will create the .csv file, add a first row with the name of each column and write a new line every time a variable changes its value.
The node is an output node and the .csv configuration can be defined with its configuration parameters.
The following image shows the configuration parameters of the subflow:
- Path: Absolute path where the file will be stored.
- Vars: List of variables that will be added to the file as columns. The time column is handled separately, do not add it here.
- Time format: Format in which the day/time information will be represented. Three options:
2020-05-18 14:00:00.000(String - ".", by default),2020-05-18 14:00:00,000(String - ",") and1589810400000(epoch) - Delimiter: Symbol to be used as a separator between columns:
,or;(,by default) - Time Name: Name to be used for the time column.
To add new values to the .csv file, it is necessary to send a message with the following format:
msg.payload = { "<var_name_1>": "<var_value_1>", "<var_name_2">: "<var_value_2>"}
It is mandatory for the variables (<var_name_1> and <var_name_2>) to have been previously declared in the Vars parameter of the node configuration.
However, it is not required to update all the variables at the same time, the message payload can contain a single or many variables.
The following image shows a complete flow:
The inject node contains the following payload:
{ "Example": 19.5 }
and the flow is executed every 5 seconds (repeat interval: every 5 seconds).
The generated .csv file can be seen below:
