Python矩陣
矩陣是二維數組的特殊情況，它的每個數據元素具有嚴格相同的大小。 所以每個矩陣也是一個二維數組，但反之亦然。 矩陣是許多數學和科學計算中非常重要的數據結構。 正如在前一章中已經討論過的二維數組結構，我們將在本章中專注於矩陣特有的數據結構操作。
也使用numpy包進行矩陣數據操作。
矩陣示例
考慮在早上，中午，晚上和深夜測量記錄1周溫度的情況。 它可以使用數組在numpy中可用的重塑方法以7 x 5矩陣的形式呈現。
from numpy import *
a = array([['Mon',18,20,22,17],['Tue',11,18,21,18],
['Wed',15,21,20,19],['Thu',11,20,22,21],
['Fri',18,17,23,22],['Sat',12,22,20,18],
['Sun',13,15,19,16]])
m = reshape(a,(7,5))
print(m)執行上面示例代碼，得到以下結果 -
[['Mon' '18' '20' '22' '17']
['Tue' '11' '18' '21' '18']
['Wed' '15' '21' '20' '19']
['Thu' '11' '20' '22' '21']
['Fri' '18' '17' '23' '22']
['Sat' '12' '22' '20' '18']
['Sun' '13' '15' '19' '16']]訪問矩陣中的值
矩陣中的數據元素可以通過使用索引來訪問。 訪問方法與在二維數組中訪問數據的方式相同。
from numpy import *
m = array([['Mon',18,20,22,17],['Tue',11,18,21,18],
['Wed',15,21,20,19],['Thu',11,20,22,21],
['Fri',18,17,23,22],['Sat',12,22,20,18],
['Sun',13,15,19,16]])
# Print data for Wednesday
print(m[2])
# Print data for friday evening
print(m[4][3])執行上面示例代碼，得到以下結果 -
['Wed' '15' '21' '20' '19']
23添加一行
from numpy import *
m = array([['Mon',18,20,22,17],['Tue',11,18,21,18],
['Wed',15,21,20,19],['Thu',11,20,22,21],
['Fri',18,17,23,22],['Sat',12,22,20,18],
['Sun',13,15,19,16]])
m_r = append(m,[['Avg',12,15,13,11]],0)
print(m_r)當上面的代碼執行時，它會產生以下結果 -
[['Mon' '18' '20' '22' '17']
['Tue' '11' '18' '21' '18']
['Wed' '15' '21' '20' '19']
['Thu' '11' '20' '22' '21']
['Fri' '18' '17' '23' '22']
['Sat' '12' '22' '20' '18']
['Sun' '13' '15' '19' '16']
['Avg' '12' '15' '13' '11']]添加一列
可以使用insert()方法將一列數據添加到矩陣。 這裏指定想要添加列的索引以及包含添加的列的新值的數組。 在下面的例子中，在開頭的第五個位置添加一個新的列。
from numpy import *
m = array([['Mon',18,20,22,17],['Tue',11,18,21,18],
['Wed',15,21,20,19],['Thu',11,20,22,21],
['Fri',18,17,23,22],['Sat',12,22,20,18],
['Sun',13,15,19,16]])
m_c = insert(m,[5],[[1],[2],[3],[4],[5],[6],[7]],1)
print(m_c)執行上面示例代碼，得到以下結果 -
[['Mon' '18' '20' '22' '17' '1']
['Tue' '11' '18' '21' '18' '2']
['Wed' '15' '21' '20' '19' '3']
['Thu' '11' '20' '22' '21' '4']
['Fri' '18' '17' '23' '22' '5']
['Sat' '12' '22' '20' '18' '6']
['Sun' '13' '15' '19' '16' '7']]從矩陣中刪除一行
可以使用delete()方法從矩陣中刪除一行。 必須指定行的索引以及行的值爲0，列的值爲1的軸值。
from numpy import *
m = array([['Mon',18,20,22,17],['Tue',11,18,21,18],
['Wed',15,21,20,19],['Thu',11,20,22,21],
['Fri',18,17,23,22],['Sat',12,22,20,18],
['Sun',13,15,19,16]])
m = delete(m,[2],0)
print(m)執行上面示例代碼，得到以下結果 -
[['Mon' '18' '20' '22' '17']
['Tue' '11' '18' '21' '18']
['Thu' '11' '20' '22' '21']
['Fri' '18' '17' '23' '22']
['Sat' '12' '22' '20' '18']
['Sun' '13' '15' '19' '16']]從Matrix中刪除一列
可以使用delete()方法從矩陣中刪除一列。 必須指定列的索引以及一行爲0，一列爲1的軸值。
from numpy import *
m = array([['Mon',18,20,22,17],['Tue',11,18,21,18],
['Wed',15,21,20,19],['Thu',11,20,22,21],
['Fri',18,17,23,22],['Sat',12,22,20,18],
['Sun',13,15,19,16]])
m = delete(m,s_[2],1)
print(m)執行上面示例代碼，得到以下結果 -
[['Mon' '18' '22' '17']
['Tue' '11' '21' '18']
['Wed' '15' '20' '19']
['Thu' '11' '22' '21']
['Fri' '18' '23' '22']
['Sat' '12' '20' '18']
['Sun' '13' '19' '16']]更新矩陣中的一行
要更新矩陣行中的值，只需在行的索引處重新分配值。 在下面的例子中，星期幾數據的所有值都標記爲0。 該行的索引是3。
from numpy import *
m = array([['Mon',18,20,22,17],['Tue',11,18,21,18],
['Wed',15,21,20,19],['Thu',11,20,22,21],
['Fri',18,17,23,22],['Sat',12,22,20,18],
['Sun',13,15,19,16]])
m[3] = ['Thu',0,0,0,0]
print(m)當上面的代碼執行時，它會產生以下結果 -
[['Mon' '18' '20' '22' '17']
['Tue' '11' '18' '21' '18']
['Wed' '15' '21' '20' '19']
['Thu' '0' '0' '0' '0']
['Fri' '18' '17' '23' '22']
['Sat' '12' '22' '20' '18']
['Sun' '13' '15' '19' '16']]