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‎.ipynb_checkpoints/Map-checkpoint.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# map()\n",
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"\n",
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"map() is a function that takes in two arguments: a function and a sequence iterable. In the form:\n",
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" map(function, sequence)\n",
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" \n",
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"The first argument is the name of a function and the second a sequence (e.g. a list). map() applies the function to all the elements of the sequence. It returns a new list with the elements changed by function.\n",
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"\n",
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"When we went over list comprehension we created a small expression to convert Fahrenheit to Celsius. Let's do the same here but use map.\n",
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"\n",
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"We'll start with two functions:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"metadata": {
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"collapsed": true
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},
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"outputs": [],
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"source": [
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"def fahrenheit(T):\n",
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" return ((float(9)/5)*T + 32)\n",
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"def celsius(T):\n",
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" return (float(5)/9)*(T-32)\n",
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" \n",
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"temp = [0, 22.5, 40,100]"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Now lets see map() in action:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 7,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"[32.0, 72.5, 104.0, 212.0]"
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]
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},
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"execution_count": 7,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"F_temps = map(fahrenheit, temp)\n",
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"\n",
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"#Show\n",
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"F_temps"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 8,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"[0.0, 22.5, 40.0, 100.0]"
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]
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},
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"execution_count": 8,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"# Convert back\n",
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"map(celsius, F_temps)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"In the example above we haven't used a lambda expression. By using lambda, we wouldn't have had to define and name the functions fahrenheit() and celsius()."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 10,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"[0.0, 22.5, 40.0, 100.0]"
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]
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},
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"execution_count": 10,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"map(lambda x: (5.0/9)*(x - 32), F_temps)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Great! We got the same result! Using map is much more commonly used with lambda expressions since the entire purpose of map() is to save effort on having to create manual for loops."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"map() can be applied to more than one iterable. The iterables have to have the same length.\n",
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"\n",
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"\n",
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"For instance, if we are working with two lists-map() will apply its lambda function to the elements of the argument lists, i.e. it first applies to the elements with the 0th index, then to the elements with the 1st index until the n-th index is reached.\n",
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"\n",
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"For example lets map a lambda expression to two lists:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 12,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"[6, 8, 10, 12]"
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]
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},
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"execution_count": 12,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"a = [1,2,3,4]\n",
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"b = [5,6,7,8]\n",
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"c = [9,10,11,12]\n",
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"\n",
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"map(lambda x,y:x+y,a,b)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 13,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"[15, 18, 21, 24]"
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]
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},
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"execution_count": 13,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"# Now all three lists\n",
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"map(lambda x,y,z:x+y+z, a,b,c)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"We can see in the example above that the parameter x gets its values from the list a, while y gets its values from b and z from list c. Go ahead and play with your own example to make sure you fully understand mapping to more than one iterable.\n",
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"\n",
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"Great job! You should now have a basic understanding of the map() function."
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.5.1"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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}

‎Map.ipynb

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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"#map()\n",
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"# map()\n",
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"\n",
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"map() is a function that takes in two arguments: a function and a sequence iterable. In the form:\n",
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" map(function, sequence)\n",
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}
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],
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"source": [
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"F_temps = map(Fahrenheit, temp)\n",
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"F_temps = map(fahrenheit, temp)\n",
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"\n",
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"#Show\n",
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"F_temps"
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 2",
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"display_name": "Python 3",
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"language": "python",
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"name": "python2"
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 2
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython2",
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"version": "2.7.10"
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"pygments_lexer": "ipython3",
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"version": "3.5.1"
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}
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},
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"nbformat": 4,

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