xticks() shifted by 1

Community matplotlib-users
1

Hi,

please consider this snippet:

import matplotlib.pyplot as plt

d={}

for i in range(1,21):

d[i] = i**2

plt.plot(d.values())

plt.xticks(d.keys())

plt.show()

As it can be seen from attached screenshot, xticks values are shifted to right (by 1).

Seems strange, but perhaps something to do with Python 0-start.

So why plot starts at beginning of x-axis and xticks start shifted by 1?

How does regular matplotlib users handle similar code?

Thanks

image.png

2

Hi,
please consider this snippet:

import matplotlib.pyplot as plt

d={}
for i in range(1,21):
   d[i] = i**2

plt.plot(d.values())

This is plotting values against the zero-based index. What you want is

plt.plot(d.keys(), d.values())

···

On 09/17/2011 09:57 AM, Klonuo Umom wrote:

plt.xticks(d.keys())
plt.show()

As it can be seen from attached screenshot, xticks values are shifted to
right (by 1).

Seems strange, but perhaps something to do with Python 0-start.
So why plot starts at beginning of x-axis and xticks start shifted by 1?
How does regular matplotlib users handle similar code?

Thanks

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3

When you called plot() with only the y values, mpl will assume x values as range(len(y)). Just call plot with both x and y values.

Ben Root

···

On Saturday, September 17, 2011, Klonuo Umom <klonuo@…287…> wrote:

Hi,
please consider this snippet:
import matplotlib.pyplot as plt
d={}

for i in range(1,21):
d[i] = i**2
plt.plot(d.values())
plt.xticks(d.keys())
plt.show()

As it can be seen from attached screenshot, xticks values are shifted to right (by 1).

Seems strange, but perhaps something to do with Python 0-start.
So why plot starts at beginning of x-axis and xticks start shifted by 1?
How does regular matplotlib users handle similar code?
Thanks

4

While this is safe because calls to keys and values will return lists
in congruent order of no intervening dict modifications are made

it is a bit fragile because there is no guarantee the dict keys will
be ordered, right, which is probably not what the OP wants. Maybe

  x = sorted(d.keys())
  y = [d[k] for k in x]
  plot(x, y)

JDH

···

On Sat, Sep 17, 2011 at 3:09 PM, Eric Firing <efiring@...202...> wrote:

On 09/17/2011 09:57 AM, Klonuo Umom wrote:

Hi,
please consider this snippet:

import matplotlib.pyplot as plt

d={}
for i in range(1,21):
d[i] = i**2

plt.plot(d.values())

This is plotting values against the zero-based index. What you want is

plt.plot(d.keys(), d.values())

5

Yes, I noticed the same and indeed I used sorted values in original problem
I forgot to add it in my simplified snippet

···

On Sat, Sep 17, 2011 at 10:34 PM, John Hunter <jdh2358@...287...> wrote:

While this is safe because calls to keys and values will return lists
in congruent order of no intervening dict modifications are made

Python dictionary: are keys() and values() always the same order? - Stack Overflow

it is a bit fragile because there is no guarantee the dict keys will
be ordered, right, which is probably not what the OP wants. Maybe

x = sorted(d.keys())
y = [d[k] for k in x]
plot(x, y)