12_Sorting_searching_and_counting.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Soring, searching, and counting"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "import numpy as np"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'1.11.2'"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "np.__version__"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "author = 'kyubyong. longinglove@nate.com'"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Sorting"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q1. Sort x along the second axis."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[[1 4]\n",
      " [1 3]]\n"
     ]
    }
   ],
   "source": [
    "x = np.array([[1,4],[3,1]])\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q2. Sort pairs of surnames and first names and return their indices. (first by surname, then by name)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[1 2 0]\n"
     ]
    }
   ],
   "source": [
    "surnames =    ('Hertz',    'Galilei', 'Hertz')\n",
    "first_names = ('Heinrich', 'Galileo', 'Gustav')\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q3. Get the indices that would sort x along the second axis."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[[0 1]\n",
      " [1 0]]\n"
     ]
    }
   ],
   "source": [
    "x = np.array([[1,4],[3,1]])\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q4. Create an array such that its fifth element would be the same as the element of sorted x, and it divide other elements by their value."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 48,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "x = [5 1 6 3 9 8 2 7 4 0]\n",
      "\n",
      "Check the fifth element of this new array is 5, the first four elements are all smaller than 5, and 6th through the end are bigger than 5\n",
      "[2 0 4 3 1 5 8 7 6 9]\n"
     ]
    }
   ],
   "source": [
    "x = np.random.permutation(10)\n",
    "print \"x =\", x\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q5. Create the indices of an array such that its third element would be the same as the element of sorted x, and it divide other elements by their value."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 56,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "x = [2 8 3 7 5 6 4 0 9 1]\n",
      "partitioned = [0 1 2 3 4 5 8 6 9 7]\n",
      "indices = [0 1 2 3 4 5 8 6 9 7]\n"
     ]
    }
   ],
   "source": [
    "x = np.random.permutation(10)\n",
    "print \"x =\", x\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Searching"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q6. Get the maximum and minimum values and their indices of x along the second axis."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 78,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "x = [[0 5 9 8 2]\n",
      " [3 7 4 1 6]]\n",
      "maximum values = [9 7]\n",
      "max indices = [2 1]\n",
      "minimum values = [0 1]\n",
      "min indices = [0 3]\n"
     ]
    }
   ],
   "source": [
    "x = np.random.permutation(10).reshape(2, 5)\n",
    "print \"x =\", x\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q7. Get the maximum and minimum values and their indices of x along the second axis, ignoring NaNs."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 79,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "maximum values ignoring NaNs = [ 4.  3.]\n",
      "max indices = [1 0]\n",
      "minimum values ignoring NaNs = [ 4.  2.]\n",
      "min indices = [1 1]\n"
     ]
    }
   ],
   "source": [
    "x = np.array([[np.nan, 4], [3, 2]])\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q8. Get the values and indices of the elements that are bigger than 2 in x.\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 113,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Values bigger than 2 = [3 3 5]\n",
      "Their indices are  (array([0, 1, 1], dtype=int64), array([2, 1, 2], dtype=int64))\n"
     ]
    }
   ],
   "source": [
    "x = np.array([[1, 2, 3], [1, 3, 5]])\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q9. Get the indices of the elements that are bigger than 2 in the flattend x."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 100,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[0 1 2 3 4 5]\n"
     ]
    }
   ],
   "source": [
    "x = np.array([[1, 2, 3], [1, 3, 5]])\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q10. Check the elements of x and return 0 if it is less than 0, otherwise the element itself."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 105,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[[0 0 0]\n",
      " [0 0 0]\n",
      " [1 2 3]]\n"
     ]
    }
   ],
   "source": [
    "x = np.arange(-5, 4).reshape(3, 3)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q11. Get the indices where elements of y should be inserted to x to maintain order."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 109,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([0, 2, 1, 3], dtype=int64)"
      ]
     },
     "execution_count": 109,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "x = [1, 3, 5, 7, 9]\n",
    "y = [0, 4, 2, 6]\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Counting"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Q12. Get the number of nonzero elements in x."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 120,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "5\n"
     ]
    }
   ],
   "source": [
    "x = [[0,1,7,0,0],[3,0,0,2,19]]\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": []
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 2",
   "language": "python",
   "name": "python2"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 2
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython2",
   "version": "2.7.10"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 0
}