title: How to replace a value in pandas, with NaN?
body: <p>I am new to pandas , I am trying to load the csv in Dataframe. My data has missing values represented as ? , and I am trying to replace it with standard Missing values - NaN</p>
  <p>Kindly help me with this . I have tried reading through Pandas docs, but I am not able to follow.</p>
  <pre class="lang-py prettyprint-override"><code>def readData(filename):
      DataLabels =[&quot;age&quot;, &quot;workclass&quot;, &quot;fnlwgt&quot;, &quot;education&quot;, &quot;education-num&quot;, &quot;marital-status&quot;,
                 &quot;occupation&quot;, &quot;relationship&quot;, &quot;race&quot;, &quot;sex&quot;, &quot;capital-gain&quot;,
                 &quot;capital-loss&quot;, &quot;hours-per-week&quot;, &quot;native-country&quot;, &quot;class&quot;] 
  
      # ==== trying to replace ? with Nan using na_values
      rawfile = pd.read_csv(filename, header=None, names=DataLabels, na_values=[&quot;?&quot;])
      age = rawfile[&quot;age&quot;]
      print(age)
      print(rawfile[25:40])
  
      #========trying to replace ?
      rawfile.replace(&quot;?&quot;, &quot;NaN&quot;)
      print(rawfile[25:40])
      return rawfile
  </code></pre>
  <pre class="lang-py prettyprint-override"><code>    age   workclass  fnlwgt      education  education-num       marital-status        occupation    relationship                 race    sex  capital-gain  capital-loss  hours-per-week  native-country   class
  25   56   Local-gov  216851      Bachelors             13   Married-civ-spouse      Tech-support         Husband                White   Male             0             0              40   United-States    &gt;50K
  26   19     Private  168294        HS-grad              9        Never-married      Craft-repair       Own-child                White   Male             0             0              40   United-States   &lt;=50K
  27   54           ?  180211   Some-college             10   Married-civ-spouse                 ?         Husband   Asian-Pac-Islander   Male             0             0              60           South    &gt;50K
  28   39     Private  367260        HS-grad              9             Divorced   Exec-managerial   Not-in-family                White   Male             0             0              80   United-States   &lt;=50K
  29   49     Private  193366        HS-grad              9   Married-civ-spouse      Craft-repair         Husband                White   Male             0             0              40   United-States   &lt;=50K
  </code></pre>
  <h2>Data</h2>
  <p><a href="http://archive.ics.uci.edu/ml/machine-learning-databases/adult/" rel="noreferrer">adult.data</a></p>
  <pre><code>39, State-gov, 77516, Bachelors, 13, Never-married, Adm-clerical, Not-in-family, White, Male, 2174, 0, 40, United-States, &lt;=50K
  50, Self-emp-not-inc, 83311, Bachelors, 13, Married-civ-spouse, Exec-managerial, Husband, White, Male, 0, 0, 13, United-States, &lt;=50K
  38, Private, 215646, HS-grad, 9, Divorced, Handlers-cleaners, Not-in-family, White, Male, 0, 0, 40, United-States, &lt;=50K
  53, Private, 234721, 11th, 7, Married-civ-spouse, Handlers-cleaners, Husband, Black, Male, 0, 0, 40, United-States, &lt;=50K
  28, Private, 338409, Bachelors, 13, Married-civ-spouse, Prof-specialty, Wife, Black, Female, 0, 0, 40, Cuba, &lt;=50K
  37, Private, 284582, Masters, 14, Married-civ-spouse, Exec-managerial, Wife, White, Female, 0, 0, 40, United-States, &lt;=50K
  49, Private, 160187, 9th, 5, Married-spouse-absent, Other-service, Not-in-family, Black, Female, 0, 0, 16, Jamaica, &lt;=50K
  52, Self-emp-not-inc, 209642, HS-grad, 9, Married-civ-spouse, Exec-managerial, Husband, White, Male, 0, 0, 45, United-States, &gt;50K
  31, Private, 45781, Masters, 14, Never-married, Prof-specialty, Not-in-family, White, Female, 14084, 0, 50, United-States, &gt;50K
  42, Private, 159449, Bachelors, 13, Married-civ-spouse, Exec-managerial, Husband, White, Male, 5178, 0, 40, United-States, &gt;50K
  37, Private, 280464, Some-college, 10, Married-civ-spouse, Exec-managerial, Husband, Black, Male, 0, 0, 80, United-States, &gt;50K
  30, State-gov, 141297, Bachelors, 13, Married-civ-spouse, Prof-specialty, Husband, Asian-Pac-Islander, Male, 0, 0, 40, India, &gt;50K
  23, Private, 122272, Bachelors, 13, Never-married, Adm-clerical, Own-child, White, Female, 0, 0, 30, United-States, &lt;=50K
  32, Private, 205019, Assoc-acdm, 12, Never-married, Sales, Not-in-family, Black, Male, 0, 0, 50, United-States, &lt;=50K
  40, Private, 121772, Assoc-voc, 11, Married-civ-spouse, Craft-repair, Husband, Asian-Pac-Islander, Male, 0, 0, 40, ?, &gt;50K
  34, Private, 245487, 7th-8th, 4, Married-civ-spouse, Transport-moving, Husband, Amer-Indian-Eskimo, Male, 0, 0, 45, Mexico, &lt;=50K
  25, Self-emp-not-inc, 176756, HS-grad, 9, Never-married, Farming-fishing, Own-child, White, Male, 0, 0, 35, United-States, &lt;=50K
  32, Private, 186824, HS-grad, 9, Never-married, Machine-op-inspct, Unmarried, White, Male, 0, 0, 40, United-States, &lt;=50K
  38, Private, 28887, 11th, 7, Married-civ-spouse, Sales, Husband, White, Male, 0, 0, 50, United-States, &lt;=50K
  43, Self-emp-not-inc, 292175, Masters, 14, Divorced, Exec-managerial, Unmarried, White, Female, 0, 0, 45, United-States, &gt;50K
  40, Private, 193524, Doctorate, 16, Married-civ-spouse, Prof-specialty, Husband, White, Male, 0, 0, 60, United-States, &gt;50K
  54, Private, 302146, HS-grad, 9, Separated, Other-service, Unmarried, Black, Female, 0, 0, 20, United-States, &lt;=50K
  35, Federal-gov, 76845, 9th, 5, Married-civ-spouse, Farming-fishing, Husband, Black, Male, 0, 0, 40, United-States, &lt;=50K
  43, Private, 117037, 11th, 7, Married-civ-spouse, Transport-moving, Husband, White, Male, 0, 2042, 40, United-States, &lt;=50K
  59, Private, 109015, HS-grad, 9, Divorced, Tech-support, Unmarried, White, Female, 0, 0, 40, United-States, &lt;=50K
  56, Local-gov, 216851, Bachelors, 13, Married-civ-spouse, Tech-support, Husband, White, Male, 0, 0, 40, United-States, &gt;50K
  19, Private, 168294, HS-grad, 9, Never-married, Craft-repair, Own-child, White, Male, 0, 0, 40, United-States, &lt;=50K
  54, ?, 180211, Some-college, 10, Married-civ-spouse, ?, Husband, Asian-Pac-Islander, Male, 0, 0, 60, South, &gt;50K
  39, Private, 367260, HS-grad, 9, Divorced, Exec-managerial, Not-in-family, White, Male, 0, 0, 80, United-States, &lt;=50K
  49, Private, 193366, HS-grad, 9, Married-civ-spouse, Craft-repair, Husband, White, Male, 0, 0, 40, United-States, &lt;=50K
  23, Local-gov, 190709, Assoc-acdm, 12, Never-married, Protective-serv, Not-in-family, White, Male, 0, 0, 52, United-States, &lt;=50K
  20, Private, 266015, Some-college, 10, Never-married, Sales, Own-child, Black, Male, 0, 0, 44, United-States, &lt;=50K
  45, Private, 386940, Bachelors, 13, Divorced, Exec-managerial, Own-child, White, Male, 0, 1408, 40, United-States, &lt;=50K
  30, Federal-gov, 59951, Some-college, 10, Married-civ-spouse, Adm-clerical, Own-child, White, Male, 0, 0, 40, United-States, &lt;=50K
  22, State-gov, 311512, Some-college, 10, Married-civ-spouse, Other-service, Husband, Black, Male, 0, 0, 15, United-States, &lt;=50K
  48, Private, 242406, 11th, 7, Never-married, Machine-op-inspct, Unmarried, White, Male, 0, 0, 40, Puerto-Rico, &lt;=50K
  21, Private, 197200, Some-college, 10, Never-married, Machine-op-inspct, Own-child, White, Male, 0, 0, 40, United-States, &lt;=50K
  19, Private, 544091, HS-grad, 9, Married-AF-spouse, Adm-clerical, Wife, White, Female, 0, 0, 25, United-States, &lt;=50K
  31, Private, 84154, Some-college, 10, Married-civ-spouse, Sales, Husband, White, Male, 0, 0, 38, ?, &gt;50K
  48, Self-emp-not-inc, 265477, Assoc-acdm, 12, Married-civ-spouse, Prof-specialty, Husband, White, Male, 0, 0, 40, United-States, &lt;=50K
  31, Private, 507875, 9th, 5, Married-civ-spouse, Machine-op-inspct, Husband, White, Male, 0, 0, 43, United-States, &lt;=50K
  53, Self-emp-not-inc, 88506, Bachelors, 13, Married-civ-spouse, Prof-specialty, Husband, White, Male, 0, 0, 40, United-States, &lt;=50K
  24, Private, 172987, Bachelors, 13, Married-civ-spouse, Tech-support, Husband, White, Male, 0, 0, 50, United-States, &lt;=50K
  49, Private, 94638, HS-grad, 9, Separated, Adm-clerical, Unmarried, White, Female, 0, 0, 40, United-States, &lt;=50K
  25, Private, 289980, HS-grad, 9, Never-married, Handlers-cleaners, Not-in-family, White, Male, 0, 0, 35, United-States, &lt;=50K
  57, Federal-gov, 337895, Bachelors, 13, Married-civ-spouse, Prof-specialty, Husband, Black, Male, 0, 0, 40, United-States, &gt;50K
  53, Private, 144361, HS-grad, 9, Married-civ-spouse, Machine-op-inspct, Husband, White, Male, 0, 0, 38, United-States, &lt;=50K
  44, Private, 128354, Masters, 14, Divorced, Exec-managerial, Unmarried, White, Female, 0, 0, 40, United-States, &lt;=50K
  41, State-gov, 101603, Assoc-voc, 11, Married-civ-spouse, Craft-repair, Husband, White, Male, 0, 0, 40, United-States, &lt;=50K
  29, Private, 271466, Assoc-voc, 11, Never-married, Prof-specialty, Not-in-family, White, Male, 0, 0, 43, United-States, &lt;=50K
  25, Private, 32275, Some-college, 10, Married-civ-spouse, Exec-managerial, Wife, Other, Female, 0, 0, 40, United-States, &lt;=50K
  18, Private, 226956, HS-grad, 9, Never-married, Other-service, Own-child, White, Female, 0, 0, 30, ?, &lt;=50K
  47, Private, 51835, Prof-school, 15, Married-civ-spouse, Prof-specialty, Wife, White, Female, 0, 1902, 60, Honduras, &gt;50K
  50, Federal-gov, 251585, Bachelors, 13, Divorced, Exec-managerial, Not-in-family, White, Male, 0, 0, 55, United-States, &gt;50K
  47, Self-emp-inc, 109832, HS-grad, 9, Divorced, Exec-managerial, Not-in-family, White, Male, 0, 0, 60, United-States, &lt;=50K
  43, Private, 237993, Some-college, 10, Married-civ-spouse, Tech-support, Husband, White, Male, 0, 0, 40, United-States, &gt;50K
  46, Private, 216666, 5th-6th, 3, Married-civ-spouse, Machine-op-inspct, Husband, White, Male, 0, 0, 40, Mexico, &lt;=50K
  35, Private, 56352, Assoc-voc, 11, Married-civ-spouse, Other-service, Husband, White, Male, 0, 0, 40, Puerto-Rico, &lt;=50K
  41, Private, 147372, HS-grad, 9, Married-civ-spouse, Adm-clerical, Husband, White, Male, 0, 0, 48, United-States, &lt;=50K
  30, Private, 188146, HS-grad, 9, Married-civ-spouse, Machine-op-inspct, Husband, White, Male, 5013, 0, 40, United-States, &lt;=50K
  30, Private, 59496, Bachelors, 13, Married-civ-spouse, Sales, Husband, White, Male, 2407, 0, 40, United-States, &lt;=50K
  32, ?, 293936, 7th-8th, 4, Married-spouse-absent, ?, Not-in-family, White, Male, 0, 0, 40, ?, &lt;=50K
  48, Private, 149640, HS-grad, 9, Married-civ-spouse, Transport-moving, Husband, White, Male, 0, 0, 40, United-States, &lt;=50K
  42, Private, 116632, Doctorate, 16, Married-civ-spouse, Prof-specialty, Husband, White, Male, 0, 0, 45, United-States, &gt;50K
  29, Private, 105598, Some-college, 10, Divorced, Tech-support, Not-in-family, White, Male, 0, 0, 58, United-States, &lt;=50K
  36, Private, 155537, HS-grad, 9, Married-civ-spouse, Craft-repair, Husband, White, Male, 0, 0, 40, United-States, &lt;=50K
  28, Private, 183175, Some-college, 10, Divorced, Adm-clerical, Not-in-family, White, Female, 0, 0, 40, United-States, &lt;=50K
  53, Private, 169846, HS-grad, 9, Married-civ-spouse, Adm-clerical, Wife, White, Female, 0, 0, 40, United-States, &gt;50K
  49, Self-emp-inc, 191681, Some-college, 10, Married-civ-spouse, Exec-managerial, Husband, White, Male, 0, 0, 50, United-States, &gt;50K
  25, ?, 200681, Some-college, 10, Never-married, ?, Own-child, White, Male, 0, 0, 40, United-States, &lt;=50K
  19, Private, 101509, Some-college, 10, Never-married, Prof-specialty, Own-child, White, Male, 0, 0, 32, United-States, &lt;=50K
  31, Private, 309974, Bachelors, 13, Separated, Sales, Own-child, Black, Female, 0, 0, 40, United-States, &lt;=50K
  29, Self-emp-not-inc, 162298, Bachelors, 13, Married-civ-spouse, Sales, Husband, White, Male, 0, 0, 70, United-States, &gt;50K
  23, Private, 211678, Some-college, 10, Never-married, Machine-op-inspct, Not-in-family, White, Male, 0, 0, 40, United-States, &lt;=50K
  79, Private, 124744, Some-college, 10, Married-civ-spouse, Prof-specialty, Other-relative, White, Male, 0, 0, 20, United-States, &lt;=50K
  </code></pre>