设计推荐算法时，首先要考虑数据格式。
由于数据是关于用户对商品的评分，其具有三个要素：用户、商品、评分
所以，数据格式有三种形式：
1. json格式(json文本)
#数据格式：json数据（用户、商品、打分）
json_txt = '''{"Angelica": {"Blues Traveler": 3.5, "Broken Bells": 2.0,
"Norah Jones": 4.5, "Phoenix": 5.0,
"Slightly Stoopid": 1.5,
"The Strokes": 2.5, "Vampire Weekend": 2.0},
"Bill":{"Blues Traveler": 2.0, "Broken Bells": 3.5,
"Deadmau5": 4.0, "Phoenix": 2.0,
"Slightly Stoopid": 3.5, "Vampire Weekend": 3.0},
"Chan": {"Blues Traveler": 5.0, "Broken Bells": 1.0,
"Deadmau5": 1.0, "Norah Jones": 3.0, "Phoenix": 5,
"Slightly Stoopid": 1.0},
"Dan": {"Blues Traveler": 3.0, "Broken Bells": 4.0,
"Deadmau5": 4.5, "Phoenix": 3.0,
"Slightly Stoopid": 4.5, "The Strokes": 4.0,
"Vampire Weekend": 2.0},
"Hailey": {"Broken Bells": 4.0, "Deadmau5": 1.0,
"Norah Jones": 4.0, "The Strokes": 4.0,
"Vampire Weekend": 1.0},
"Jordyn": {"Broken Bells": 4.5, "Deadmau5": 4.0,
"Norah Jones": 5.0, "Phoenix": 5.0,
"Slightly Stoopid": 4.5, "The Strokes": 4.0,
"Vampire Weekend": 4.0},
"Sam": {"Blues Traveler": 5.0, "Broken Bells": 2.0,
"Norah Jones": 3.0, "Phoenix": 5.0,
"Slightly Stoopid": 4.0, "The Strokes": 5.0},
"Veronica": {"Blues Traveler": 3.0, "Norah Jones": 5.0,
"Phoenix": 4.0, "Slightly Stoopid": 2.5,
"The Strokes": 3.0}
}'''
2. 矩阵格式(csv文本)
横轴是商品，纵轴是用户，表内是评分
#数据格式：矩阵（用户-商品）（适用于小数据量）
csv_txt = '''"user","Blues Traveler","Broken Bells","Deadmau5","Norah Jones","Phoenix","Slightly Stoopid","The Strokes","Vampire Weekend"
"Angelica",3.5,2.0,,4.5,5.0,1.5,2.5,2.0
"Bill",2.0,3.5,4.0,,2.0,3.5,,3.0
"Chan",5.0,1.0,1.0,3.0,5,1.0,,
"Dan",3.0,4.0,4.5,,3.0,4.5,4.0,2.0
"Hailey",,4.0,1.0,4.0,,,4.0,1.0
"Jordyn",,4.5,4.0,5.0,5.0,4.5,4.0,4.0
"Sam",5.0,2.0,,3.0,5.0,4.0,5.0,
"Veronica",3.0,,,5.0,4.0,2.5,3.0,'''
3. 条目格式(csv文本)
每一行代表一条记录，其形式为：用户，商品，打分
#数据格式：条目（用户、商品、打分）（避免巨型稀疏矩阵）
csv_txt = '''"Angelica","Blues Traveler",3.5
"Angelica","Broken Bells",2.0
"Angelica","Norah Jones",4.5
"Angelica","Phoenix",5.0
"Angelica","Slightly Stoopid",1.5
"Angelica","The Strokes",2.5
"Angelica","Vampire Weekend",2.0
"Bill","Blues Traveler",2.0
"Bill","Broken Bells",3.5
"Bill","Deadmau5",4.0
"Bill","Phoenix",2.0
"Bill","Slightly Stoopid",3.5
"Bill","Vampire Weekend",3.0
"Chan","Blues Traveler",5.0
"Chan","Broken Bells",1.0
"Chan","Deadmau5",1.0
"Chan","Norah Jones",3.0
"Chan","Phoenix",5,
"Chan","Slightly Stoopid",1.0
"Dan","Blues Traveler",3.0
"Dan","Broken Bells",4.0
"Dan","Deadmau5",4.5
"Dan","Phoenix",3.0
"Dan","Slightly Stoopid",4.5
"Dan","The Strokes",4.0
"Dan","Vampire Weekend",2.0
"Hailey","Broken Bells",4.0
"Hailey","Deadmau5",1.0
"Hailey","Norah Jones",4.0
"Hailey","The Strokes",4.0
"Hailey","Vampire Weekend",1.0
"Jordyn","Broken Bells",4.5
"Jordyn","Deadmau5",4.0
"Jordyn","Norah Jones",5.0
"Jordyn","Phoenix",5.0
"Jordyn","Slightly Stoopid",4.5
"Jordyn","The Strokes",4.0
"Jordyn","Vampire Weekend",4.0
"Sam","Blues Traveler",5.0
"Sam","Broken Bells",2.0
"Sam","Norah Jones",3.0
"Sam","Phoenix",5.0
"Sam","Slightly Stoopid",4.0
"Sam","The Strokes",5.0
"Veronica","Blues Traveler",3.0
"Veronica","Norah Jones",5.0
"Veronica","Phoenix",4.0
"Veronica","Slightly Stoopid",2.5
"Veronica","The Strokes",3.0'''