{"id":4507,"date":"2022-08-15T08:13:30","date_gmt":"2022-08-15T08:13:30","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=4507"},"modified":"2022-08-16T06:16:52","modified_gmt":"2022-08-16T06:16:52","slug":"numpy-vstack","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-numpy\/numpy-vstack\/","title":{"rendered":"NumPy vstack()"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the NumPy vstack()<\/code> function to vertically join elements of two or more arrays into a single array.<\/p>\n\n\n\n

Introduction to the NumPy vstack() function #<\/a><\/h2>\n\n\n\n

The vstack()<\/code> function joins elements of two or more arrays<\/a> into a single array vertically (row-wise).<\/p>\n\n\n\n

Here’s the syntax of the vstack()<\/code> function:<\/p>\n\n\n

numpy.vstack((a1,a2,...))<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In this syntax, the (a1, a2, …) is a sequence of arrays with the ndarray<\/code> type. <\/p>\n\n\n\n
All arrays a1, a2, .. must have the same shape along all but the first axis. If they’re 1D arrays, then they must have the same length.<\/p>\n\n\n\n
NumPy vstack() function examples #<\/a><\/h2>\n\n\n\n
Let’s take some examples of using the vstack()<\/code> function.<\/p>\n\n\n\n
1) Using vstack() function to join elements of 1D arrays #<\/a><\/h3>\n\n\n\n
The following example uses the vstack()<\/code> function to join two 1D arrays vertically:<\/p>\n\n\n
import<\/span> numpy as<\/span> np\n\na = np.array([1<\/span>, 2<\/span>])\nb = np.array([3<\/span>, 4<\/span>])\n\nc = np.vstack((a, b))\nprint(c)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
[[1<\/span> 2<\/span>] \n [3<\/span> 4<\/span>]]<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
\"numpy<\/figure>\n\n\n\n
Note that for 1D arrays, all input arrays must have the same length or you’ll get an error.<\/p>\n\n\n\n
The following example attempts to join elements of two 1D arrays with different lengths and causes an error:<\/p>\n\n\n
import<\/span> numpy as<\/span> np\n\na = np.array([1<\/span>, 2<\/span>])\nb = np.array([3<\/span>, 4<\/span>, 5<\/span>])\n\nc = np.vstack((a, b))\nprint(c)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Error:<\/p>\n\n\n
ValueError: all the input array dimensions for<\/span> the concatenation axis must match exactly, but along dimension 1<\/span>, the array at index 0<\/span> has size 2<\/span> and<\/span> the array at index 1<\/span> has size 3<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
<\/p>\n\n\n\n
2) Using vstack() function to join elements of 2D arrays #<\/a><\/h3>\n\n\n\n
The following example uses the vstack()<\/code> function to join elements of two 2D arrays:<\/p>\n\n\n
import<\/span> numpy as<\/span> np\n\na = np.array([\n    [1<\/span>, 2<\/span>],\n    [3<\/span>, 4<\/span>]\n])\nb = np.array([\n    [5<\/span>, 6<\/span>],\n    [7<\/span>, 8<\/span>]\n])\n\nc = np.vstack((a, b))\nprint(c)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
\"numpy<\/figure>\n\n\n\n
Output:<\/p>\n\n\n
[[1<\/span> 2<\/span>] \n [3<\/span> 4<\/span>] \n [5<\/span> 6<\/span>] \n [7<\/span> 8<\/span>]]<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
  • Use the numpy vstack()<\/code> function to join two or more arrays vertically.<\/li><\/ul>\n
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