Matplotlib ValueError x and y must have same first dimension

Question

I am trying to fit a linear line of best fit to my matplotlib graph  I keep getting the error that x and y do not have the same first dimension  But they both have lengths of 15  What am I doing wrong   import matplotlib pyplot as plt from scipy import stats import numpy as np  x    0 46 0 59 0 68 0 99 0 39 0 31 1 09 0 77 0 72 0 49 0 55 0 62 0 58 0 88 0 78  y    0 315 0 383 0 452 0 650 0 279 0 215 0 727 0 512 0 478 0 335 0 365 0 424 0 390 0 585 0 511  xerr    0 01  15 yerr    0 001  15  plt rc  font   family  serif   size 13  m  b   np polyfit x  y  1  plt plot x y  s  color   0066FF   plt plot x  m x   b   r-    BREAKS ON THIS LINE plt errorbar x y xerr xerr yerr 0 linestyle  None  color  black   plt xlabel    Delta t    s    fontsize 20  plt ylabel    Delta p    hPa    fontsize 20  plt autoscale enable True  axis u both   tight False  plt grid False  plt xlim 0 2 1 2  plt ylim 0 0 8  plt show

User · Answer

Changing your lists to numpy arrays will do the job         import matplotlib pyplot as plt from scipy import stats import numpy as np   x   np array  0 46 0 59 0 68 0 99 0 39 0 31 1 09 0 77 0 72 0 49 0 55 0 62 0 58 0 88 0 78     x is a numpy array now y   np array  0 315 0 383 0 452 0 650 0 279 0 215 0 727 0 512 0 478 0 335 0 365 0 424 0 390 0 585 0 511     y is a numpy array now xerr    0 01  15 yerr    0 001  15  plt rc  font   family  serif   size 13  m  b   np polyfit x  y  1  plt plot x y  s  color   0066FF   plt plot x  m x   b   r-    BREAKS ON THIS LINE plt errorbar x y xerr xerr yerr 0 linestyle  None  color  black   plt xlabel    Delta t    s    fontsize 20  plt ylabel    Delta p    hPa    fontsize 20  plt autoscale enable True  axis u both   tight False  plt grid False  plt xlim 0 2 1 2  plt ylim 0 0 8  plt show

User · Answer

You should make x and y numpy arrays  not lists   x   np array  0 46 0 59 0 68 0 99 0 39 0 31 1 09                0 77 0 72 0 49 0 55 0 62 0 58 0 88 0 78   y   np array  0 315 0 383 0 452 0 650 0 279 0 215 0 727 0 512                0 478 0 335 0 365 0 424 0 390 0 585 0 511     With this change  it produces the expect plot  If they are lists  m   x will not produce the result you expect  but an empty list  Note that m is  anumpy float64 scalar  not a standard Python float   I actually consider this a bit dubious behavior of Numpy  In normal Python  multiplying a list with an integer just repeats the list   In  42   2    1  2  3  Out 42    1  2  3  1  2  3    while multiplying a list with a float gives an error  as I think it should    In  43   1 5    1  2  3  --------------------------------------------------------------------------- TypeError                                 Traceback  most recent call last   lt ipython-input-43-d710bb467cdd gt  in  lt module gt    ---- gt  1 1 5    1  2  3  TypeError  can t multiply sequence by non-int of type  float    The weird thing is that multiplying a Python list with a Numpy scalar apparently works   In  45   np float64 0 5     1  2  3  Out 45       In  46   np float64 1 5     1  2  3  Out 46    1  2  3   In  47   np float64 2 5     1  2  3  Out 47    1  2  3  1  2  3    So it seems that the float gets truncated to an int  after which you get the standard Python behavior of repeating the list  which is quite unexpected behavior  The best thing would have been to raise an error  so that you would have spotted the problem yourself instead of having to ask your question on Stackoverflow  or to just show the expected element-wise multiplication  in which your code would have just worked   Interestingly  addition between a list and a Numpy scalar does work   In  69   np float64 0 123     1  2  3  Out 69   array   1 123   2 123   3 123

[python] Matplotlib: ValueError: x and y must have same first dimension

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