Python Plot Drawing parallel diagonal lines using data, not axis limits

Question

I want to draw parallel diagonal lines. The second diagonal line should be 5% below the first one and the third one should be 5% above the first one. I do not want to use the axis limits because my data is not stationary, it is volatile. So, I want to use actual limits. My code works fine and produces the output. Whether this is the correct approach or not I have no idea. I mean, 5% below 1200 is 1200*0.95 but how to get 5% below at close to the origin. In my code, I have used 50 by trial and error.

My code and output:

plt.plot([0,1200],[50,1200*1.05],'k--',linewidth=2)
plt.plot([0,1200],[0,1200],'k--',linewidth=2)
plt.plot([50,1200],[0,1200*0.95],'k--',linewidth=2)

You can't recalculate every y value as a percentage as this will just change the gradient of the line. You need to ADD the same amount to EVERY y value (or minus) to shift it up or down while keeping the same gradient — GhandiFloss
– GhandiFloss, Commented Sep 11, 2020 at 14:04
@GhandiFloss Thanks a ton. Yes! I figured out that suppose 5% of 1000 is 50. I should use this number to the plot below and above lines. Your comment reassured me. THanks — Mainland
– Mainland, Commented Sep 11, 2020 at 14:07
print(1200+(1200*(5/100))) print(1200-(1200*(5/100))) for 5+% and 5-% .Hence consider x as your number i.e. 1200 — Karthik
– Karthik, Commented Sep 11, 2020 at 14:10

Valdi_Bo · Accepted Answer · 2020-09-11 15:15:24Z

1

To draw diagonal lines, regardless of the current x / y limits, the most natural approach is to:

specify ending poins of lines in axes coordinates (0 to 1),
pass transform=ax.transAxes.

Running the following example code:

fig = plt.figure()
ax = plt.subplot(xlim=(0, 1250), ylim=(0, 1200))
ax.text(0.05, 0.95, 'Diagonal lines', transform=ax.transAxes, fontsize=12, va='top')
# Diagonal
plt.plot([0,    1],    [0,    1],    'k--', linewidth=1, transform=ax.transAxes)
# 5 % down
plt.plot([0.05, 1],    [0,    0.95], 'r--', linewidth=1, transform=ax.transAxes)
# 5 % up
plt.plot([0,    0.95], [0.05, 1],    'g--', linewidth=1, transform=ax.transAxes)
plt.show()

I got the following plot:

I deliberately used different colors of lines, to ease their identification.

Experiment with this code, changing xlim and ylim, and each time all 3 lines should be at just the same positions.

answered Sep 11, 2020 at 15:15

Valdi_Bo

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Another.Chemist Over a year ago

I am interested on your answer. How can one define the limits, x and y of the dashed lines?

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