NbClust: no visible global function definition for ‘na.omit’
NbClust: no visible global function definition for ‘dist’
NbClust: no visible global function definition for ‘hclust’
NbClust : Dis: no visible global function definition for ‘dist’
NbClust : Index.Hubert: no visible global function definition for
  ‘dist’
NbClust : Index.Hubert: no visible global function definition for ‘var’
NbClust : Index.sPlussMoins: no visible global function definition for
  ‘as.dist’
NbClust : Index.sPlussMoins: no visible global function definition for
  ‘median’
NbClust : Index.15and28: no visible global function definition for
  ‘as.dist’
NbClust : Indice.ptbiserial : biserial.cor: no visible global function
  definition for ‘complete.cases’
NbClust : Indice.ptbiserial : biserial.cor: no visible global function
  definition for ‘sd’
NbClust : Indices.WBT: no visible global function definition for ‘cov’
NbClust : Indice.DB: no visible global function definition for ‘dist’
NbClust : Indice.Gap : GAP : simgap: no visible global function
  definition for ‘runif’
NbClust : Indice.Gap : GAP: no visible global function definition for
  ‘kmeans’
NbClust : Indice.Gap : GAP: no visible global function definition for
  ‘cutree’
NbClust : Indice.Gap : GAP: no visible global function definition for
  ‘hclust’
NbClust : Indice.Gap : GAP: no visible global function definition for
  ‘dist’
NbClust : Indice.Gap : GAP: no visible global function definition for
  ‘var’
NbClust: no visible global function definition for ‘cutree’
NbClust: no visible global function definition for ‘kmeans’
NbClust: no visible global function definition for ‘pf’
NbClust: no visible global function definition for ‘par’
NbClust: no visible global function definition for ‘plot’
Undefined global functions or variables:
  as.dist complete.cases cov cutree dist hclust kmeans median na.omit
  par pf plot runif sd var
Consider adding
  importFrom("graphics", "par", "plot")
  importFrom("stats", "as.dist", "complete.cases", "cov", "cutree",
             "dist", "hclust", "kmeans", "median", "na.omit", "pf",
             "runif", "sd", "var")
to your NAMESPACE file.