Ways to concatenate two lists in Python

concatenate() function concatenate a sequence of arrays along an existing axis.

1. Syntax : numpy.concatenate((arr1, arr2, …), axis=0, out=None)
2. Parameters :
3. arr1, arr2, … : [sequence of array_like] The arrays must have the same shape, except in the dimension corresponding to axis.

concatenate. Concatenation refers to joining. This function is used to join two or more arrays of the same shape along a specified axis.

NumPy’s concatenate function can be used to concatenate two arrays either row-wise or column-wise. Concatenate function can take two or more arrays of the same shape and by default it concatenates row-wise i.e. axis=0. The resulting array after row-wise concatenation is of the shape 6 x 3, i.e. 6 rows and 3 columns.

In general it is better/faster to iterate or append with lists, and apply the np. array (or concatenate) just once. appending to a list is fast; much faster than making a new array.

1. Method #1 : Using Naive Method.
2. Method #2 : Using + operator.
3. Method #3 : Using list comprehension.
4. Method #4 : Using extend()
5. Method #5 : Using * operator.
6. Method #6 : Using itertools.chain()

Python Join Two Lists

1. ❮ Python Glossary.
2. Example. Join two list:
3. Example. Append list2 into list1:
4. Example. Use the extend() method to add list2 at the end of list1:
5. Related Pages.
6. ❮ Python Glossary.

You can concatenate two or more 1d arrays using the vstack and hstack methods. concatenate() is more efficient than these methods. concatenate() also supports concatenating 2d, 3d, and higher dimension arrays.

Yes, by default, concatenating dataframes will preserve their row order. The order of the dataframes to concatenate will be the order of the result dataframe.