How to use for loop to plot in subplots in Python

Question

Example Input Data:

I am a beginner in python. I use for loop to read several csv files look like above(all of those file are same format).

so far my code was look like below.

import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
import os

pd.set_option('display.max_columns', None)
pd.set_option('display.max_rows', None)

ax, fig = plt.subplots(4,4,sharex=False, sharey=False, figsize=(22, 10), dpi=70, linewidth=0.5)
ax = np.array(ax)

def loop_directory(directory):
    for filename in os.listdir(directory):
        if filename.endswith(".csv"):
            file_directory = os.path.join(directory, filename)
            # print(filename)
            df = pd.read_csv(file_directory)

            df = df[df['Tavg'].isin([-999]) == False]

            df[['Year','Month']] = df[['Year','Month']].astype(int).astype(str)
            df["Year&Month"] = df[['Year', 'Month']].agg("/".join,axis=1)

            df["Year&Month"] = pd.to_datetime(df["Year&Month"])
            x = df["Year&Month"]
            y = df["Tavg"]

            for axes,col in zip(x, y):
                axes.plot(df.index, df[col]) # here is the problem, i dont know how to use for loop to plot in subplots
    plt.show()

if __name__ == "__main__":
   loop_directory(r"C:\Users\LAB312\Desktop\vietnam\anomaly")

I've tried for ten more times but didn't work at all.

I want to know how to use those syntaxes ex. ax zip ,etc.

enter image description here

I want to plot in every subplot in one plot. it should have plot every ax.

Answer 1

Firstly, you have your fig and ax reversed in your call to plt.subplots, it should be:

fig, ax = plt.subplots(4,4,sharex=False, sharey=False, figsize=(22, 10), dpi=70, linewidth=0.5)

You can then access each set of axes to call plot by indexing. You can index the 4 by 4 numpy array to get each axes set in your 4 by 4 grid of plots. i.e. ax[0, 0].plot(...), ax[0, 1].plot(...), etc. up to ax[3, 3].plot(...)

Your question needs a bit more information to clarify how you want the data plotted though! I can see you combine the first two columns so that you have 4 columns, but consider how do you want each sample to be plotted.

---

EDIT: As you want to plot your files sequentially in ax[0, 0], ax[0, 1], etc., you can flatten the 2D numpy array of axes to get a 1D iterable that you can loop through or index with one value. I don't have your files so I can't test it but here's some demo code that should give you an idea of what to do.

As @sam mentioned in the comments, you should seperate your csv collection logic and your plotting logic.

def loop_directory(directory):
    # Get all files, filter for '.csv' and prepend dir path
    files = os.listdir(directory)
    csvs = [os.path.join(directory, f) for f in files if f.endswith('.csv')]
    return csvs

def plot_csvs(csvs):
    fig, ax = plt.subplots(4, 4, sharex=False, sharey=False, figsize=(22, 10), dpi=70, linewidth=0.5)
    ax = np.array(ax).flatten()  # Flatten to 1D, [0 ,0], [0, 1], etc

    # This assumes number of subplots >= number of CSVs
    for i, filename in enumerate(csvs):
        df = pd.read_csv(filename)

        # Do your processing here

        x = df["Year&Month"]
        y = df["Tavg"]

        ax[i].plot(x, y)

    plt.show()
    
csv_dir = '/path/to/csv/dir'
csv_paths = loop_directory(csv_dir)
plot_csvs(csv_paths)