netgrossplot: no visible binding for global variable ‘changes’
Undefined global functions or variables:
  changes
netgrossplot: no visible binding for global variable ‘changes’
Undefined global functions or variables:
  changes
netgrossplot: no visible binding for global variable ‘changes’
Undefined global functions or variables:
  changes
netgrossplot: no visible binding for global variable ‘changes’
Undefined global functions or variables:
  changes
netgrossplot: no visible binding for global variable 'changes'
Undefined global functions or variables:
  changes
netgrossplot: no visible binding for global variable ‘changes’
Undefined global functions or variables:
  changes
netgrossplot: no visible binding for global variable ‘changes’
Undefined global functions or variables:
  changes
netgrossplot: no visible binding for global variable 'changes'
Undefined global functions or variables:
  changes
netgrossplot: no visible binding for global variable 'changes'
Undefined global functions or variables:
  changes