title: Python/Sklearn - Value Error: could not convert string to float
body: <p>I'm trying to run a kNN classifier across my dataset using 10-fold CV. I have some experience with models in WEKA but struggling to transfer this over to Sklearn.</p>
  
  <p>Below is my code</p>
  
  <pre><code>filename = 'train4.csv'
  names = ['attribute names are here']
  
  df = pandas.read_csv(filename, names=names)
  
  num_folds = 10
  kfold = KFold(n_splits=10, random_state=7)
  model = KNeighborsClassifier()
  results = cross_val_score(model, df.drop('mix1_instrument', axis=1), df['mix1_instrument'], cv=kfold)
  print(results.mean())
  </code></pre>
  
  <p>I am receiving this error </p>
  
  <pre><code> ValueError: could not convert string to float: ''
  </code></pre>
  
  <p>How can I convert this attribute? And this contains useful information for classifying my instances would a conversion impact this?</p>
  
  <p>There are two attributes that are 'object' that I believe need converting named 'class1' and class2'</p>
  
  <p>Sample data below...</p>
  
  <pre><code>{
      'temporalCentroid': {
          0: 'temporalCentroid',
          1: '1.67324',
          2: '1.330722',
          3: '0.786984',
          4: '1.850129'
      },
      'LogSpecCentroid': {
          0: 'LogSpecCentroid',
          1: '-1.043802',
          2: '-0.82943',
          3: '-2.441297',
          4: '-0.837145'
      },
      'LogSpecSpread': {
          0: 'LogSpecSpread',
          1: '0.747558',
          2: '1.378373',
          3: '0.667634',
          4: '1.238404'
      },
      'MFCC1': {
          0: 'MFCC1',
          1: '3.502117',
          2: '6.697601',
          3: '4.011488',
          4: '0.823614'
      },
      'MFCC2': {
          0: 'MFCC2',
          1: '-9.208897',
          2: '-9.741549',
          3: '15.27665',
          4: '-15.22256'
      },
      'MFCC3': {
          0: 'MFCC3',
          1: '-2.334097',
          2: '-9.868089',
          3: '0.802509',
          4: '-4.978688'
      },
      'MFCC4': {
          0: 'MFCC4',
          1: '-9.013086',
          2: '0.609091',
          3: '2.50685',
          4: '-2.489553'
      },
      'MFCC5': {
          0: 'MFCC5',
          1: '4.847481',
          2: '1.733307',
          3: '0.10459',
          4: '1.066615'
      },
      'MFCC6': {
          0: 'MFCC6',
          1: '-4.770421',
          2: '-5.381835',
          3: '-0.260118',
          4: '-1.020861'
      },
      'MFCC7': {
          0: 'MFCC7',
          1: '-3.362488',
          2: '-1.261088',
          3: '0.593255',
          4: '-2.007349'
      },
      'MFCC8': {
          0: 'MFCC8',
          1: '-9.527529',
          2: '-3.809237',
          3: '-0.362287',
          4: '-8.938164'
      },
      'MFCC9': {
          0: 'MFCC9',
          1: '-9.629579',
          2: '1.486923',
          3: '-2.957592',
          4: '-2.324424'
      },
      'MFCC10': {
          0: 'MFCC10',
          1: '1.848685',
          2: '-3.938455',
          3: '-1.884439',
          4: '-2.535579'
      },
      'MFCC11': {
          0: 'MFCC11',
          1: '-2.311295',
          2: '-2.159865',
          3: '-0.827179',
          4: '0.638553'
      },
      'MFCC12': {
          0: 'MFCC12',
          1: '-7.696675',
          2: '-3.138412',
          3: '-0.605056',
          4: '-1.116259'
      },
      'MFCC13': {
          0: 'MFCC13',
          1: '10.35572',
          2: '9.095669',
          3: '6.426399',
          4: '15.04535'
      },
      'MFCCMin': {
          0: 'MFCCMin',
          1: '-9.629579',
          2: '-9.868089',
          3: '-2.957592',
          4: '-15.22256'
      },
      'MFCCMax': {
          0: 'MFCCMax',
          1: '10.35572',
          2: '9.095669',
          3: '15.27665',
          4: '15.04535'
      },
      'MFCCSum': {
          0: 'MFCCSum',
          1: '-37.300064',
          2: '-19.675939',
          3: '22.82507',
          4: '-23.059305'
      },
      'MFCCAvg': {
          0: 'MFCCAvg',
          1: '-2.869235692',
          2: '-1.513533769',
          3: '1.755774615',
          4: '-1.773792692'
      },
      'MFCCStd': {
          0: 'MFCCStd',
          1: '6.409842944',
          2: '5.558499123',
          3: '4.756836281',
          4: '6.76039911'
      },
      'Energy': {
          0: 'Energy',
          1: '-2.96148',
          2: '-3.522993',
          3: '-3.409359',
          4: '-2.235853'
      },
      'ZeroCrossings': {
          0: 'ZeroCrossings',
          1: '128',
          2: '188',
          3: '43',
          4: '288'
      },
      'SpecCentroid': {
          0: 'SpecCentroid',
          1: '284.0513',
          2: '414.8489',
          3: '102.2096',
          4: '405.1262'
      },
      'SpecSpread': {
          0: 'SpecSpread',
          1: '207.5526',
          2: '350.7937',
          3: '53.52178',
          4: '360.0353'
      },
      'Rolloff': {
          0: 'Rolloff',
          1: '263.7817',
          2: '783.2703',
          3: '129.1992',
          4: '912.4695'
      },
      'Flux': {
          0: 'Flux',
          1: '0',
          2: '0',
          3: '0',
          4: '0'
      },
      'bandsCoefMin': {
          0: 'bandsCoefMin',
          1: '-0.224957',
          2: '-0.247903',
          3: '-0.22283',
          4: '-0.232534'
      },
      'bandsCoefMax': {
          0: 'bandsCoefMax',
          1: '-0.074945',
          2: '-0.113654',
          3: '-0.062254',
          4: '-0.080883'
      },
      'bandsCoefSum1': {
          0: 'bandsCoefSum1',
          1: '-5.575428',
          2: '-5.524777',
          3: '-5.511125',
          4: '-5.532536'
      },
      'bandsCoefAvg': {
          0: 'bandsCoefAvg',
          1: '-0.168952364',
          2: '-0.167417485',
          3: '-0.167003788',
          4: '-0.167652606'
      },
      'bandsCoefStd': {
          0: 'bandsCoefStd',
          1: '0.042580181',
          2: '0.048429973',
          3: '0.049881374',
          4: '0.0475839'
      },
      'bandsCoefSum': {
          0: 'bandsCoefSum',
          1: '382.5963',
          2: '360.9232',
          3: '384.3541',
          4: '368.9903'
      },
      'prjmin': {
          0: 'prjmin',
          1: '-0.999362',
          2: '-0.999719',
          3: '-0.988315',
          4: '-0.999421'
      },
      'prjmax': {
          0: 'prjmax',
          1: '0.023797',
          2: '0.009596',
          3: '0.028112',
          4: '0.024612'
      },
      'prjSum': {
          0: 'prjSum',
          1: '-0.99911',
          2: '-1.006792',
          3: '-1.084054',
          4: '-1.002478'
      },
      'prjAvg': {
          0: 'prjAvg',
          1: '-0.030276061',
          2: '-0.030508848',
          3: '-0.032850121',
          4: '-0.030378121'
      },
      'prjStd': {
          0: 'prjStd',
          1: '0.174082468',
          2: '0.174040569',
          3: '0.173600498',
          4: '0.174064118'
      },
      'LogAttackTime': {
          0: 'LogAttackTime',
          1: '0.365883',
          2: '-0.35427',
          3: '-0.669283',
          4: '-0.026181'
      },
      'HamoPkMin': {
          0: 'HamoPkMin',
          1: '0',
          2: '0',
          3: '0',
          4: '0'
      },
      'HamoPkMax': {
          0: 'HamoPkMax',
          1: '1.025473',
          2: '1.05761',
          3: '0.986766',
          4: '0.957316'
      },
      'HamoPkSum': {
          0: 'HamoPkSum',
          1: '14.391206',
          2: '20.306125',
          3: '9.727358',
          4: '14.772449'
      },
      'HamoPkAvg': {
          0: 'HamoPkAvg',
          1: '0.513971643',
          2: '0.72521875',
          3: '0.347405643',
          4: '0.527587464'
      },
      'HamoPkStd': {
          0: 'HamoPkStd',
          1: '0.376622124',
          2: '0.325929503',
          3: '0.388971641',
          4: '0.381693476'
      },
      'class1': {
          0: 'class1',
          1: 'aerophone',
          2: 'aerophone',
          3: 'chordophone',
          4: 'aerophone'
      },
      'class2': {
          0: 'class2',
          1: 'aero_single-reed',
          2: 'aero_lip-vibrated',
          3: 'chrd_simple',
          4: 'aero_single-reed'
      },
      'mix1_instrument': {
          0: 'mix1_instrument',
          1: 'Saxophone',
          2: 'Trumpet',
          3: 'Piano',
          4: 'Clarinet'
      }
  }
  </code></pre>
  
  <p>Thanks </p>