lightgbm.basic.LightGBMError: Label should be the first column in a LibSVM file

[unavailableun]

If both train data and valid data exists, below exception will be raised up when constructing valid data.
It will succeed if only train data exists.

 File "/opt/miniconda/lib/python3.7/site-packages/lightgbm/engine.py", line 275, in train
    booster.add_valid(valid_set, name_valid_set)
  File "/opt/miniconda/lib/python3.7/site-packages/lightgbm/basic.py", line 2945, in add_valid
    data.construct().handle))
  File "/opt/miniconda/lib/python3.7/site-packages/lightgbm/basic.py", line 1811, in construct
    feature_name=self.feature_name, params=self.params)
  File "/opt/miniconda/lib/python3.7/site-packages/lightgbm/basic.py", line 1528, in _lazy_init
    ctypes.byref(self.handle)))
  File "/opt/miniconda/lib/python3.7/site-packages/lightgbm/basic.py", line 132, in _safe_call
    raise LightGBMError(_LIB.LGBM_GetLastError().decode('utf-8'))
lightgbm.basic.LightGBMError: Label should be the first column in a LibSVM file

[chjinche]

Fixed PR has been merged in Jan.