def extract(inputdata,variables,taxon):
    """Extract/filter inputdata for the specified variables and taxon
    
    Parameters
    ---------- 
        'inputdata' (pandas df): Biological and environmental measurements
                            columns: ["ID","taxon","abundance","variable","value"]

        'variables' (pandas df): List of considered variables
                            columns: ["variable","name_sim',"consider"] 
        'taxon' (str): name of the taxon    
        
    Returns
    -------
        'inputdata' (pandas df): Biological and environmental measurements
                            columns: ["ID","taxon","abundance","variable","value"]               
    """
    
    "Extract data for taxon and variables "
    inputdata = inputdata[inputdata["variable"].isin(variables)]
    inputdata = inputdata[inputdata["taxon"]==taxon]
    "Remove NaN values"
    inputdata = inputdata[~inputdata["value"].isnull()]
    #inputdata["value"] = inputdata["value"].astype(float)
    
      
    return inputdata