How can wildcards be preserved while expanding a dictionary in Snakemake?

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To preserve wildcards while expanding a dictionary in Snakemake, you can use the expand function with the wildcards parameter. Here's an example:

rule example:
    input:
        "input/{sample}/file_{num}.txt"
    output:
        "output/{sample}/result_{num}.out"
    params:
        param_dict=lambda wildcards: {"sample": wildcards.sample, "num": wildcards.num}
    shell:
        "command --input {input} --output {output} --params {params}"

expanded_inputs = expand("input/{sample}/file_{num}.txt", sample=["A", "B"], num=[1, 2])
expanded_outputs = expand("output/{sample}/result_{num}.out", wildcards, sample=["A", "B"], num=[1, 2])
params_dict = {"sample": "{sample}", "num": "{num}"}

rule example:
    input:
        input=expanded_inputs
    output:
        output=expanded_outputs
    params:
        params_dict=params_dict
    shell:
        "command --input {input} --output {output} --params {params}"

In this example, we use the expand function to generate the input and output file paths with wildcards. We then pass the wildcards object into the expand function for the output paths, which preserves the values of the wildcards. Finally, we use a params_dict dictionary to pass the values of the sample and num wildcards as parameters to the shell command.