How to create a numpy array of arbitrary length strings

Question

I m a complete rookie to Python  but it seems like a given string is able to be  effectively  arbitrary length   i e  you can take a string str and keeping adding to it  str     some stuff       Is there a way to make an array of such strings   When I try this  each element only stores a single character  strArr   numpy empty 10  dtype  string   for i in range 0 10      strArr i     test    On the other hand  I know I can initialize an array of certain length strings  i e   strArr   numpy empty 10  dtype  s256     which can store 10 strings of up to 256 characters

User · Answer

You could use the object data type    gt  gt  gt  import numpy  gt  gt  gt  s   numpy array   a    b    dude    dtype  object    gt  gt  gt  s 0      bcdef   gt  gt  gt  s array  abcdef  b  dude   dtype object

User · Answer

You can do so by creating an array of dtype object  If you try to assign a long string to a normal numpy array  it truncates the string    gt  gt  gt  a   numpy array   apples    foobar    cowboy     gt  gt  gt  a 2     bananas   gt  gt  gt  a array   apples    foobar    banana           dtype   S6     But when you use dtype object  you get an array of python object references  So you can have all the behaviors of python strings    gt  gt  gt  a   numpy array   apples    foobar    cowboy    dtype object   gt  gt  gt  a array  apples  foobar  cowboy   dtype object   gt  gt  gt  a 2     bananas   gt  gt  gt  a array  apples  foobar  bananas   dtype object    Indeed  because it s an array of objects  you can assign any kind of python object to the array    gt  gt  gt  a 2     1 2  3 4   gt  gt  gt  a array  apples  foobar   1  2  3  4    dtype object    However  this undoes a lot of the benefits of using numpy  which is so fast because it works on large contiguous blocks of raw memory  Working with python objects adds a lot of overhead  A simple example    gt  gt  gt  a   numpy array   abba  for   in range 10000     gt  gt  gt  b   numpy array   abba  for   in range 10000    dtype object   gt  gt  gt   timeit a copy   100000 loops  best of 3  2 51 us per loop  gt  gt  gt   timeit b copy   10000 loops  best of 3  48 4 us per loop

[python] How to create a numpy array of arbitrary length strings?

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