一行代码练习题 --- 数据处理

FreddyMusic

有一组数据，精度太高，小数点后四位。
现将它重新处理，仅要保留小数点后两位。

你如何处理？

1. 
   
2. Points = {{119.7442, 40.1175}, {119.7947, 39.9667}, {119.7539,
   
3.     40.0092}, {119.7356, 40.0328}, {119.55, 40.2}, {119.2833,
   
4.     40.15}, {119.025, 40.1256}, {119.5564, 40.2169}, {119.4956,
   
5.     40.1242}, {119.6683, 40.2242}, {118.9344, 40.14}, {118.8333,
   
6.     40.1667}, {118.8167, 40.1833}, {118.7253, 40.1978}, {118.5456,
   
7.     40.4069}, {118.4011, 40.2931}, {118.2889, 40.4167}, {118.2667,
   
8.     40.4333}, {118.25, 40.4333}, {118.0878, 40.3497}, {118.9483,
   
9.     40.2817}, {117.8767, 40.2764}, {117.6944, 40.1825}, {117.4556,
   
10.     40.2464}, {117.4394, 40.2422}, {117.35, 40.2833}, {117.2667,
    
11.     40.4833}, {117.2333, 40.4}, {117.3625, 40.675}, {117.2853,
    
12.     40.6578}, {117.2361, 40.6833}, {117.155, 40.6889}, {116.8839,
    
13.     40.7669}, {116.8839, 40.7308}, {116.8747, 40.6203}, {116.85,
    
14.     40.55}, {116.6583, 40.4417}, {116.5619, 40.4381}, {116.5028,
    
15.     40.4556}, {116.4942, 40.4625}, {116.4064, 40.4528}, {116.4536,
    
16.     40.4594}, {116.3333, 40.4}, {116.3389, 40.4169}, {116.3269,
    
17.     40.4144}, {116.3069, 40.4119}, {116.3014, 40.4117}, {116.1131,
    
18.     40.2264}, {116.0686, 40.2881}, {116.0317, 40.3372}, {116.0064,
    
19.     40.3544}, {115.1639, 39.42}, {114.8794, 40.81}, {114.9631,
    
20.     39.4889}, {113.905, 37.8933}, {113.9, 39.3167}, {113.8778,
    
21.     37.9669}, {113.2886, 40.0789}, {111.4903, 39.435}, {113.0869,
    
22.     39.9142}, {113.0833, 39.9108}, {109.7367, 38.2889}, {107.5892,
    
23.     37.5942}, {111.6575, 40.8247}, {106.2733, 38.4336}, {105.1744,
    
24.     37.5144}, {103.7775, 36.0694}, {102.6333, 37.9333}, {101.0264,
    
25.     38.7975}, {100.4653, 38.9331}, {98.5125, 39.74}, {98.2778,
    
26.     39.8}, {98.2161, 39.8014}, {98.2, 39.7433}, {94.6633,
    
27.     40.1372}, {93.8642, 40.3536}, {119.7441, 40.1176}, {118.9344,
    
28.     40.1413}, {119.4954, 40.1242}, {119.7947, 39.9666}, {119.7355,
    
29.     40.0329}, {119.7504, 40.0066}, {119.6684, 40.2242}, {119.5562,
    
30.     40.217}, {118.0875, 40.3498}, {117.9482, 40.2816}, {118.7253,
    
31.     40.1978}, {118.3201, 40.423}, {113.8776, 37.967}, {113.9049,
    
32.     37.8933}};
    

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[ 本帖最后由 FreddyMusic 于 2008-11-14 16:27 编辑 ]

gyzhou

In[11]:= Timing[Round[points*100.]/100.]
Out[11]= {2.75387*10^-17, {{119.74, 40.12}, {119.79, 39.97}, {119.75,
   40.01}, {119.74, 40.03}, {119.55, 40.2}, {119.28, 40.15}, {119.02,
   40.13}, {119.56, 40.22}, {119.5, 40.12}, {119.67, 40.22}, {118.93,
   40.14}, {118.83, 40.17}, {118.82, 40.18}, {118.73, 40.2}, {118.55,
   40.41}, {118.4, 40.29}, {118.29, 40.42}, {118.27, 40.43}, {118.25,
   40.43}, {118.09, 40.35}, {118.95, 40.28}, {117.88, 40.28}, {117.69,
    40.18}, {117.46, 40.25}, {117.44, 40.24}, {117.35,
   40.28}, {117.27, 40.48}, {117.23, 40.4}, {117.36, 40.67}, {117.29,
   40.66}, {117.24, 40.68}, {117.16, 40.69}, {116.88, 40.77}, {116.88,
    40.73}, {116.87, 40.62}, {116.85, 40.55}, {116.66,
   40.44}, {116.56, 40.44}, {116.5, 40.46}, {116.49, 40.46}, {116.41,
   40.45}, {116.45, 40.46}, {116.33, 40.4}, {116.34, 40.42}, {116.33,
   40.41}, {116.31, 40.41}, {116.3, 40.41}, {116.11, 40.23}, {116.07,
   40.29}, {116.03, 40.34}, {116.01, 40.35}, {115.16, 39.42}, {114.88,
    40.81}, {114.96, 39.49}, {113.9, 37.89}, {113.9, 39.32}, {113.88,
   37.97}, {113.29, 40.08}, {111.49, 39.44}, {113.09, 39.91}, {113.08,
    39.91}, {109.74, 38.29}, {107.59, 37.59}, {111.66,
   40.82}, {106.27, 38.43}, {105.17, 37.51}, {103.78, 36.07}, {102.63,
    37.93}, {101.03, 38.8}, {100.47, 38.93}, {98.51, 39.74}, {98.28,
   39.8}, {98.22, 39.8}, {98.2, 39.74}, {94.66, 40.14}, {93.86,
   40.35}, {119.74, 40.12}, {118.93, 40.14}, {119.5, 40.12}, {119.79,
   39.97}, {119.74, 40.03}, {119.75, 40.01}, {119.67, 40.22}, {119.56,
    40.22}, {118.09, 40.35}, {117.95, 40.28}, {118.73, 40.2}, {118.32,
    40.42}, {113.88, 37.97}, {113.9, 37.89}}}

marveloustau

1. In[29]:= Timing@
   
2. Map[N[FromDigits[RealDigits[#]], RealDigits[#][[2]] + 2] &,
   
3.   Points, {-1}]
   
4. 
   
5. Out[29]= {0.016001, {{119.74, 40.12}, {119.79, 39.97}, {119.75,
   
6.    40.01}, {119.74, 40.03}, {119.55, 40.20}, {119.28, 40.15}, {119.03,
   
7.     40.13}, {119.56, 40.22}, {119.50, 40.12}, {119.67,
   
8.    40.22}, {118.93, 40.14}, {118.83, 40.17}, {118.82, 40.18}, {118.73,
   
9.     40.20}, {118.55, 40.41}, {118.40, 40.29}, {118.29,
   
10.    40.42}, {118.27, 40.43}, {118.25, 40.43}, {118.09, 40.35}, {118.95,
    
11.     40.28}, {117.88, 40.28}, {117.69, 40.18}, {117.46,
    
12.    40.25}, {117.44, 40.24}, {117.35, 40.28}, {117.27, 40.48}, {117.23,
    
13.     40.40}, {117.36, 40.68}, {117.29, 40.66}, {117.24,
    
14.    40.68}, {117.16, 40.69}, {116.88, 40.77}, {116.88, 40.73}, {116.87,
    
15.     40.62}, {116.85, 40.55}, {116.66, 40.44}, {116.56,
    
16.    40.44}, {116.50, 40.46}, {116.49, 40.46}, {116.41, 40.45}, {116.45,
    
17.     40.46}, {116.33, 40.40}, {116.34, 40.42}, {116.33,
    
18.    40.41}, {116.31, 40.41}, {116.30, 40.41}, {116.11, 40.23}, {116.07,
    
19.     40.29}, {116.03, 40.34}, {116.01, 40.35}, {115.16,
    
20.    39.42}, {114.88, 40.81}, {114.96, 39.49}, {113.91, 37.89}, {113.90,
    
21.     39.32}, {113.88, 37.97}, {113.29, 40.08}, {111.49,
    
22.    39.44}, {113.09, 39.91}, {113.08, 39.91}, {109.74, 38.29}, {107.59,
    
23.     37.59}, {111.66, 40.82}, {106.27, 38.43}, {105.17,
    
24.    37.51}, {103.78, 36.07}, {102.63, 37.93}, {101.03, 38.80}, {100.47,
    
25.     38.93}, {98.51, 39.74}, {98.28, 39.80}, {98.22, 39.80}, {98.20,
    
26.    39.74}, {94.66, 40.14}, {93.86, 40.35}, {119.74, 40.12}, {118.93,
    
27.    40.14}, {119.50, 40.12}, {119.79, 39.97}, {119.74, 40.03}, {119.75,
    
28.     40.01}, {119.67, 40.22}, {119.56, 40.22}, {118.09,
    
29.    40.35}, {117.95, 40.28}, {118.73, 40.20}, {118.32, 40.42}, {113.88,
    
30.     37.97}, {113.90, 37.89}}}
    
31. 
    
32. In[30]:= Timing[Round[Points*100.]/100.]
    
33. 
    
34. Out[30]= {0.004001, {{119.74, 40.12}, {119.79, 39.97}, {119.75,
    
35.    40.01}, {119.74, 40.03}, {119.55, 40.2}, {119.28, 40.15}, {119.02,
    
36.    40.13}, {119.56, 40.22}, {119.5, 40.12}, {119.67, 40.22}, {118.93,
    
37.    40.14}, {118.83, 40.17}, {118.82, 40.18}, {118.73, 40.2}, {118.55,
    
38.    40.41}, {118.4, 40.29}, {118.29, 40.42}, {118.27, 40.43}, {118.25,
    
39.    40.43}, {118.09, 40.35}, {118.95, 40.28}, {117.88, 40.28}, {117.69,
    
40.     40.18}, {117.46, 40.25}, {117.44, 40.24}, {117.35,
    
41.    40.28}, {117.27, 40.48}, {117.23, 40.4}, {117.36, 40.67}, {117.29,
    
42.    40.66}, {117.24, 40.68}, {117.16, 40.69}, {116.88, 40.77}, {116.88,
    
43.     40.73}, {116.87, 40.62}, {116.85, 40.55}, {116.66,
    
44.    40.44}, {116.56, 40.44}, {116.5, 40.46}, {116.49, 40.46}, {116.41,
    
45.    40.45}, {116.45, 40.46}, {116.33, 40.4}, {116.34, 40.42}, {116.33,
    
46.    40.41}, {116.31, 40.41}, {116.3, 40.41}, {116.11, 40.23}, {116.07,
    
47.    40.29}, {116.03, 40.34}, {116.01, 40.35}, {115.16, 39.42}, {114.88,
    
48.     40.81}, {114.96, 39.49}, {113.9, 37.89}, {113.9, 39.32}, {113.88,
    
49.    37.97}, {113.29, 40.08}, {111.49, 39.44}, {113.09, 39.91}, {113.08,
    
50.     39.91}, {109.74, 38.29}, {107.59, 37.59}, {111.66,
    
51.    40.82}, {106.27, 38.43}, {105.17, 37.51}, {103.78, 36.07}, {102.63,
    
52.     37.93}, {101.03, 38.8}, {100.47, 38.93}, {98.51, 39.74}, {98.28,
    
53.    39.8}, {98.22, 39.8}, {98.2, 39.74}, {94.66, 40.14}, {93.86,
    
54.    40.35}, {119.74, 40.12}, {118.93, 40.14}, {119.5, 40.12}, {119.79,
    
55.    39.97}, {119.74, 40.03}, {119.75, 40.01}, {119.67, 40.22}, {119.56,
    
56.     40.22}, {118.09, 40.35}, {117.95, 40.28}, {118.73, 40.2}, {118.32,
    
57.     40.42}, {113.88, 37.97}, {113.9, 37.89}}}
    

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对比了一下, gyzhou同学给出的方法比我的在时间上快了4倍...不过印象中末位的0作为有效数字是不应该舍去的...但一Round就没了

waynebuaa

我这个，看着好像是达到要求了，。。。。。。:lol

1. 
   
2. In[2]:= Timing@
   
3. Table[{SetPrecision[Points[[i, 1]], 5],
   
4.    SetPrecision[Points[[i, 2]], 4]}, {i, Length[Points]}]
   
5. 
   
6. Out[2]= {0., {{119.74, 40.12}, {119.79, 39.97}, {119.75,
   
7.    40.01}, {119.74, 40.03}, {119.55, 40.20}, {119.28, 40.15}, {119.03,
   
8.     40.13}, {119.56, 40.22}, {119.50, 40.12}, {119.67,
   
9.    40.22}, {118.93, 40.14}, {118.83, 40.17}, {118.82, 40.18}, {118.73,
   
10.     40.20}, {118.55, 40.41}, {118.40, 40.29}, {118.29,
    
11.    40.42}, {118.27, 40.43}, {118.25, 40.43}, {118.09, 40.35}, {118.95,
    
12.     40.28}, {117.88, 40.28}, {117.69, 40.18}, {117.46,
    
13.    40.25}, {117.44, 40.24}, {117.35, 40.28}, {117.27, 40.48}, {117.23,
    
14.     40.40}, {117.36, 40.67}, {117.29, 40.66}, {117.24,
    
15.    40.68}, {117.16, 40.69}, {116.88, 40.77}, {116.88, 40.73}, {116.87,
    
16.     40.62}, {116.85, 40.55}, {116.66, 40.44}, {116.56,
    
17.    40.44}, {116.50, 40.46}, {116.49, 40.46}, {116.41, 40.45}, {116.45,
    
18.     40.46}, {116.33, 40.40}, {116.34, 40.42}, {116.33,
    
19.    40.41}, {116.31, 40.41}, {116.30, 40.41}, {116.11, 40.23}, {116.07,
    
20.     40.29}, {116.03, 40.34}, {116.01, 40.35}, {115.16,
    
21.    39.42}, {114.88, 40.81}, {114.96, 39.49}, {113.91, 37.89}, {113.90,
    
22.     39.32}, {113.88, 37.97}, {113.29, 40.08}, {111.49,
    
23.    39.44}, {113.09, 39.91}, {113.08, 39.91}, {109.74, 38.29}, {107.59,
    
24.     37.59}, {111.66, 40.82}, {106.27, 38.43}, {105.17,
    
25.    37.51}, {103.78, 36.07}, {102.63, 37.93}, {101.03, 38.80}, {100.47,
    
26.     38.93}, {98.513, 39.74}, {98.278, 39.80}, {98.216,
    
27.    39.80}, {98.200, 39.74}, {94.663, 40.14}, {93.864, 40.35}, {119.74,
    
28.     40.12}, {118.93, 40.14}, {119.50, 40.12}, {119.79,
    
29.    39.97}, {119.74, 40.03}, {119.75, 40.01}, {119.67, 40.22}, {119.56,
    
30.     40.22}, {118.09, 40.35}, {117.95, 40.28}, {118.73,
    
31.    40.20}, {118.32, 40.42}, {113.88, 37.97}, {113.90, 37.89}}}
    

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[ 本帖最后由 waynebuaa 于 2008-11-14 22:05 编辑 ]

FreddyMusic

都搞得不赖，发点小分，鼓励鼓励。