title: what does it mean for 'threshold the data'?
body: <p>I came across a online data mining course project</p>
  
  <p><a href="http://www.kdnuggets.com/data_mining_course/assignments/final-project.html" rel="nofollow">http://www.kdnuggets.com/data_mining_course/assignments/final-project.html</a></p>
  
  <p>The data is of samples with 7000 features as genes. Each gene is associated with a value. Some of the values are negative. The data looks like in this way:</p>
  
  <p>SNO "U48730_at" "U58516_at" "U73738_at" "X06956_at" "X16699_at" "X83863_at"</p>
  
  <p>X1   "  27"      " 161"      "   0"      "  34"      "   2"      " 116"<br>
  X2   "  27"      " 265"      "   0"      "  98"      "   2"      " 123"<br>
  X3   "  24"      " 126"      "   0"      "  21"      "   0"      " 142"<br>
  X4   "  27"      " 163"      "  -1"      "  16"      "  -1"      " 134"<br>
  X5   "  41"      " 138"      "   1"      "  29"      "   1"      " 153"<br>
  X6   "  55"      " 107"      "  -1"      "  17"      "   0"      " 152"<br>
  X7   "  27"      "  99"      "   0"      "  57"      "   1"      " 139"<br>
  X8   "   2"      " 137"      "  -1"      "  19"      "  -3"      " 213"<br>
  X9   "   -5"     "  161"     "   -3"     "   23"     "    2"     "  193"<br>
  X10  "   0"      " 110"      "  -3"      "   7"      "  -1"      " 208"<br>
  X11  "  -7"      "  67"      "   1"      "   2"      "  -2"      " 149"<br>
  X12  "   4"      "  93"      "   3"      "  37"      "   2"      " 266"<br>
  X13  "    2"     "   75"     "    3"     "   30"     "    6"     "  205" </p>
  
  <p>The professor advise the students to first do 'data cleaning'. The original sentence is 
   Threshold both train and test data to a minimum value of 20, maximum of 16,000. </p>
  
  <p>I first thought that it is to search over each gene and if there is a value out of the bounds, then just discard this gene as a feature. However, it seems for every gene, there must be a sample with the value out of bound.</p>
  
  <p>What should I do by "threshold this data"? Is that like if the value is below 20, then set it 20 or if the value is above 16000, then just set it as 16000? </p>
  
  <p>Thanks in advance!</p>