Python for loop matplotlib 条形图不显示所有数据

Question

I have a dictionary where each key represents a year, and each value represents a rainfall anomaly over a certain domain for that year.

anoms_yearly.keys()

dict_keys([1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019])

Each key, value pair is simply an xarray dataarray, which has the value and the time of the value.

anoms_yearly[1980].values
array(-3.49641086)

Now, I try and plot the data in a simple bar graph.

fig,ax=plt.subplots(figsize=(20,12))
for i in anoms_yearly.keys():
    if anoms_yearly[i].values<0:
        colors='brown'
    else:
        colors='green'
    ax.bar(anoms_yearly[i]['time'], anoms_yearly[i].values, color=colors)

Here, anoms_yearly[i]['time'] represents one year, as it loops through time and anoms_yearly[i].values is just a single array with one value. The plot is missing all sorts of bars and randomly plots a few. What is going on here?

Answer 1

I am a bit puzzled what you do with the keys and entries of your dictionary in the plotting function. Let's create a minimum working example:

import matplotlib.pyplot as plt
import random

D = dict()
for i in range(1900,2000):
    D[str(i)] = random.random()-0.5

The dictionary D contains the years from 1900-1999 as strings as keys and a random number between -0.5 and 0.5 as corresponding values.

You can loop through the keys of the dictionary as you did. But if you want access it, just call the dictionary with the key. There is no need to do this sort of indexing and calling .values() and .keys() afterwards again. See:

fig,ax = plt.subplots()
for key in D.keys():
    if D[key] < 0:
        colors='brown'
    else:
        colors='green'
    ax.bar(key, D[key], color=colors)

The xticks are now messed up because they are strings and python/matplotlib does not know that they are ordered and can be grouped...

anyway, I guess that your odd output came from the strange indexing anoms_yearly[i]['time'] , where I frankly don't understand why you index it with the key (in the case there D[key] and index the return again with time as if another dictionary would be returned...)