code: def pick_rois(rois_img, roi_values, bg_val=0):
      
      img = read_img(rois_img)
      img_data = img.get_data()
  
      if bg_val == 0:
          out = np.zeros(img_data.shape, dtype=img_data.dtype)
      else:
          out = np.ones(img_data.shape, dtype=img_data.dtype) * bg_val
  
      for r in roi_values:
          out[img_data == r] = r
  
      return nib.Nifti2Image(out, affine=img.affine, header=img.header)
docs: Return the `rois_img` only with the ROI values from `roi_values`.
      Parameters
      ----------
      rois_img: niimg-like
  
      roi_values: list of int or float
          The list of values from rois_img.
  
      bg_val: int or float
          The background value of `rois_img`.
  
      Returns
      -------
      subset_rois_img: nibabel.Nifti2Image