I am trying to find an elegant way to loop over a series of files contained in a folder. I tried implementing community examples (https://www.knime.com/nodeguide/control-structures/loops/example-for-reading-a-list-of-files) and a few variants, but I keep getting an error that says: Errors loading flow variables into node : Coding issue: Cannot create URL of data file from \my_folder.
I created a flow variable in the List Files Node. My understanding is that this will create a list My_list, pass it onto the file reader (which I set to use My_list as the variable). The node throws an error telling me that the “DataUrl” parameter is controlled by a variable. Isn’t this exactly what I am trying to/supposed to do?
In the file location browser it says that the input location is a directory, not the list of files I want to loop over. How can i fix this?
The Table Row To Variable Loop Start node will automatically create a variable out of the list passed on by the List Files node, so no need to create the My_list variable. Simply select the folder in the List Files node that you want to scan, add any filters and your loop will go through all of those outputs in the File Reader. Just choose for example the URL column in the File Reader node as the location of the files you want to read.
I am using Table to row variable loop start node and it works fine. But how if the folder contains many different file types and you only want to read .txt files?
Simply treat the list of files as any other record type and use a Row Filter to select only the .txt files for further processing before the Table Row To Variable Loop Start node.
You don’t need a Row Filter. You can manage the files to select directly in the List Files node. If it’s not in the dropdow list, just type it in.
gr. Hans
