docstr: read tracks with specific indices
          
docstr_tok: ["read","tracks","with","specific","indices"]
code: def read_tracksi(self, indices):
      """read tracks with specific indices"""
      tracks = Streamlines()
      for i in indices:
          off0, off1 = self.offsets[i : i + 2]
          tracks.append(self.tracks[off0:off1])
      return tracks
  
file_path: dipy/dipy/io/dpy.py
imports: import numpy
  import h5py
  from nibabel.streamlines import ArraySequence
label_desc: Use image node_id 6 for calling the Dpy obj's underlying member method code with example usage: obj.read_tracksi(indices) and returns: tracks