Concatenate a NumPy array to another NumPy array

Question

I have a numpy array  Something like   a b c    And then I want to concatenate it with another NumPy array  just like we create a list of lists   How do we create a NumPy array containing NumPy arrays  I tried to do the following without any luck  gt  gt  gt  M   np array      gt  gt  gt  M array     dtype float64   gt  gt  gt  M append a axis 0  Traceback  most recent call last    File  quot  lt stdin gt  quot   line 1  in  lt module gt  AttributeError   numpy ndarray  object has no attribute  append   gt  gt  gt  a array  1  2  3

User · Answer

Try this code   import numpy as np  a1   np array      n   int input  quot  quot     for i in range 0 n       a   int input  quot  quot        a1   np append a  a1      a   0  print a1   Also you can use array instead of  quot a quot

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I had the same issue  and I couldn t comment on  Sven Marnach answer  not enough rep  gosh I remember when Stackoverflow first started     anyway   Adding a list of random numbers to a 10 X 10 matrix   myNpArray   np zeros  1  10   for x in range 1 11 1       randomList    list np random randint 99  size 10        myNpArray   np vstack  myNpArray  randomList   myNpArray   myNpArray 1     Using np zeros   an array is created with 1 x 10 zeros   array   0   0   0   0   0   0   0   0   0   0       Then a list of 10 random numbers is created using np random and assigned to randomList  The loop stacks it 10 high  We just have to remember to remove the first empty entry   myNpArray  array   31   10   19   78   95   58    3   47   30   56            51   97    5   80   28   76   92   50   22   93            64   79    7   12   68   13   59   96   32   34            44   22   46   56   73   42   62    4   62   83            91   28   54   69   60   95    5   13   60   88            71   90   76   53   13   53   31    3   96   57            33   87   81    7   53   46    5    8   20   71            46   71   14   66   68   65   68   32    9   30             1   35   96   92   72   52   88   86   94   88            13   36   43   45   90   17   38    1   41   33       So in a function   def array matrix random range  array size       myNpArray   np zeros  1  array size       for x in range 1  array size   1  1           randomList    list np random randint random range  size array size            myNpArray   np vstack  myNpArray  randomList       return myNpArray 1     a 7 x 7 array using random numbers 0 - 1000  array matrix 1000  7   array   621   377   931   180   964   885   723            298   382   148   952   430   333   956            398   596   732   422   656   348   470            735   251   314   182   966   261   523            373   616   389    90   884   957   826            587   963    66   154   111   529   945            950   413   539   860   634   195   915

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If I understand your question  here s one way   Say you have   a    4 1  6 21  1 0    so here s some code      def array in array scalarlist       return   x   for x in scalarlist    Which leads to    In  72   a    4 1  6 21  1 0   In  73   a Out 73    4 1  6 21  1 0   In  74   def array in array scalarlist                return   x   for x in scalarlist             In  75   b   array in array a   In  76   b Out 76     4 1     6 21     1 0

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In  1   import numpy as np  In  2   a   np array   1  2  3    4  5  6     In  3   b   np array   9  8  7    6  5  4     In  4   np concatenate  a  b   Out 4    array   1  2  3           4  5  6           9  8  7           6  5  4      or this   In  1   a   np array  1  2  3    In  2   b   np array  4  5  6    In  3   np vstack  a  b   Out 3    array   1  2  3           4  5  6

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Well  the error message says it all   NumPy arrays do not have an append   method   There s a free function numpy append   however   numpy append M  a    This will create a new array instead of mutating M in place   Note that using numpy append   involves copying both arrays   You will get better performing code if you use fixed-sized NumPy arrays

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Sven said it all  just be very cautious because of automatic type adjustments when append is called   In  2   import numpy as np  In  3   a   np array  1 2 3    In  4   b   np array  1  2  3     In  5   c   np array   a   b   c     In  6   np append a b  Out 6   array   1    2    3    1    2    3     In  7   a dtype Out 7   dtype  int64    In  8   np append a c  Out 8    array   1    2    3    a    b    c           dtype   S1     As you see based on the contents the dtype went from int64 to float32  and then to S1

User · Answer

Actually one can always create an ordinary list of numpy arrays and convert it later   In  1   import numpy as np  In  2   a   np array   1 2   3 4     In  3   b   np array   1 2   3 4     In  4   l    a   In  5   l append b   In  6   l   np array l   In  7   l shape Out 7    2  2  2   In  8   l Out 8    array    1  2            3  4              1  2            3  4

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You may use numpy append        import numpy  B   numpy array  3   A   numpy array  1  2  2   B   numpy append  B   A    print B   gt   3 1 2 2    This will not create two separate arrays but will append two arrays into a single dimensional array

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I found this link while looking for something slightly different  how to start appending array objects to an empty numpy array  but tried all the solutions on this page to no avail  Then I found this question and answer  How to add a new row to an empty numpy array The gist here   The way to  quot start quot  the array that you want is  arr   np empty  0 3   int   Then you can use concatenate to add rows like so  arr   np concatenate    arr    x  y  z       axis 0  See also https   docs scipy org doc numpy reference generated numpy concatenate html

[python] Concatenate a NumPy array to another NumPy array

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