# Plot Horizontal Line in Python

Rana Hasnain Khan May 17, 2022

We will introduce how to create a horizontal line in Python. We will also introduce the `Matplotlib` library in Python.

## Horizontal Line in Python

A horizontal line is any straight line that drives from left to right or right to left. When we see it in a coordinate plane, it is a line parallel to the x-axis.

In Python, `Matplotlib` is popularly used for plotting. There are many methods available to plot a horizontal line which is as follows.

1. Plotting horizontal line by the `plot()` function.
2. Plotting horizontal lines by the `hlines()` function.
3. Plotting horizontal line by the `axhline()` function.

## Use the `plot()` Function in Python

When our goal is to produce 2D plots, we can use the `Plot()` function. X points are x-axis points towards the plot, and Y points are y-axis points.

Code:

``````# python
import matplotlib.pyplot as plotLine

xAxis = [3, 5, 7, 9]
yAxis = [0, 0, 0, 0]
plotLine.plot(xAxis,yAxis)
plotLine.show()
``````

Output: First, we imported the `matplotlib.pyplot` library, then outlined the data points we wanted to plot. In this example, we stated the y-axis points to be 0 because our goal is to draw a horizontal line.

We apply the `plotLine.plot()` function to draw a line, and for visual purposes, we have used `plotLine.show()`.

## Use the `hlines()` Function in Python

When we want to draw a horizontal line across the axes, we use the `hlines()` function. This function will simplify our task.

Syntax:

``````# python
hlines(Yaxis, XaxisStart, XaxisEnd, lineColor, lineStyle)
``````

Here, four parameters are used, `Yaxis` will denote the position on the y-axis when we need to plot a line. `XaxisStart` and `XaxisEnd` indicate where the line starts and where it will end.

The `lineColor` will add the required colors to the line, and the `lineStyle` will add the style or type of the line we specified.

Code:

``````# python
import matplotlib.pyplot as plotLine

plotLine.hlines(3, 5, 10, color='blue')
plotLine.show()
``````

Output: We used the `matplotlib.pyplot` library to create a horizontal line with the help of the `hlines()` function. As an argument, we have passed the values and got the result as shown above.

## Use the `axhline()` Function in Python

The `axhline()` function is designed to draw horizontal lines to the plot. The `axhline()` function has similar parameters as in `hlines()` function.

Code:

``````# python
import matplotlib.pyplot as plotLine

plotLine.axhline(y=1.3, xmin=0.2, xmax=0.7)
plotLine.show()
``````

Output: We have drawn a horizontal line and authorized the `y`, `xmin`, and `xmax` as parameters and fixed them as 1.3, 0.2, and 0.7.

## Dotted Horizontal Line in Python

`Matplotlib` library also allows us to have a dotted line. When we need a dotted horizontal line, we have to change the line style to a dotted line, which will do the trick for us.

The `Matplotlib.pyplot` library offers the `linestyle` parameter to set the line type.

Code:

``````# python
import matplotlib.pyplot as plotLine

plotLine.axhline(y=1.3, xmin=0.2, xmax=0.7, linestyle='dotted')
plotLine.show()
``````

Output: The `axhline()` function have four parameters `y`, `xmin`, `xmax`, and `linestyle`. Our goal is to achieve a horizontal line dotted in style, so we fixed `linestyle` to dotted.

## Horizontal Line With Label in Python

We can also achieve a horizontal line with a label with the help of the `axhline()` function. We have to set the `label` as a parameter.

Code:

``````# python
import matplotlib.pyplot as plotLine

plotLine.axhline(y=1.3, xmin=0.2, xmax=0.7, label= 'Line Label')
plotLine.legend(loc='upper left')
plotLine.show()
``````

Output: We can easily create a label for the horizontal line by using the `label` parameter. We can define the label’s location using another function, `legend()`.

## Multiple Horizontal Line Matplotlib

We can also achieve multiple horizontal lines in `matplotlib` in Python. There are two methods available by which we can achieve our goal, using the `axhline()` method or by using the `hlines()` method.

`Axhline()` method allows us to obtain multiple horizontal lines in the plot.

Code:

``````# python
import matplotlib.pyplot as plotLine

plotLine.axhline(y=1.3, xmin=0.2, xmax=0.7, label= 'Blue Line Label')
plotLine.legend(loc='upper left')
plotLine.axhline(y=1.8, xmin=0.6, xmax=0.9, label= 'Red Line Label', color="red")
plotLine.legend(loc='upper left')
plotLine.axhline(y=1.5, xmin=0.5, xmax=0.9, label= 'Yellow Line Label', color="yellow")
plotLine.legend(loc='upper left')
plotLine.show()
``````

Output: Rana is a computer science graduate passionate about helping people to build and diagnose scalable web application problems and problems developers face across the full-stack.