38 c |
38 c |
39 |
39 |
40 to access the element 23 we type |
40 to access the element 23 we type |
41 c[1][2] |
41 c[1][2] |
42 |
42 |
43 It is second row third column of c. Note that index values of arrays also start from 0. |
43 It is the second row, third column of c. Note that index values of arrays also start from 0. |
44 Alternative and popular way of doing this is |
44 Alternative and popular way of doing this is |
45 c[1, 2] |
45 c[1, 2] |
46 |
46 |
47 here ',' is used as separator for row and column value. Similarly any value from the array can be accessed. |
47 here ',' is used as separator for row and column value. Similarly any value from the array can be accessed. |
48 |
48 |
60 as we can see, second row all elements are now 0 |
60 as we can see, second row all elements are now 0 |
61 |
61 |
62 Accessing a row is straight forward we skip column part |
62 Accessing a row is straight forward we skip column part |
63 but to access whole column we have to use |
63 but to access whole column we have to use |
64 c[:,2] |
64 c[:,2] |
65 will return third column. |
65 it returns third column. |
66 here the ':' part mentioned for row value symbolises entire row. |
66 here the ':' part mentioned for row value means entire row. |
67 the c[1] we were using earlier can also be written as c[1,:] |
67 the c[1] we were using earlier can also be written as c[1,:] |
68 |
68 |
69 ':' actually takes two value. for any row or column we can mention |
69 ':' actually takes two value. for any row or column we can mention start:end values, and rows/columns starting for 'start' till 'end' will be returned. Lets try some examples for better understanding |
70 start:end values, and rows/columns starting for 'start' till 'end' will be returned. Lets try some examples for better understanding |
|
71 c[0:2,:] |
70 c[0:2,:] |
72 will result in rows starting from first(0) till second and all columns. Note here that 'end' in our case, '2' would not be included in resulting array. |
71 will result in 2x3 array with rows starting from first(0) till second and all columns. Note here that 'end', in our case, '2' would not be included in resulting array. |
73 |
72 |
74 c[1:3,:] |
73 c[1:3,:] |
75 gives second and third row. |
74 gives second and third row. |
76 |
75 |
77 similarly we can try this on columns also: |
76 similarly we can try this on columns also: |
81 There is one more interesting and handy feature of slicing. We saw earlier that how only ':' means entire row or column. |
80 There is one more interesting and handy feature of slicing. We saw earlier that how only ':' means entire row or column. |
82 It actually means if we don't specify start and end part of slice default is from zero to end. |
81 It actually means if we don't specify start and end part of slice default is from zero to end. |
83 |
82 |
84 so |
83 so |
85 c[:, :2] |
84 c[:, :2] |
86 will also give us first two columns |
85 will also give us the first two columns |
87 and c[:, 1:] will return last columns. |
86 and c[:, 1:] will return last columns of c |
88 |
87 |
89 c[1:, :2] |
88 c[1:, :2] |
90 returns first two columns of last two rows |
89 returns first two columns of last two rows |
91 |
90 |
92 Now we will look into one more powerful feature of arrays: 'striding'. |
91 Now we will look into one more powerful feature of arrays: 'striding'. |