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Tag: python (Page 9 of 26)

Learning Guitar with Python, Part 1

After many years of just messing around, I’ve started formal guitar lessons this year. A lot of my instruction includes learning the notes on the fret board, the different keys of music, scales, some basic music theory, and so forth. I’ve taken a lot of hand written notes during my instructional sessions and recently started transcribing a lot of those digitally. It occurred to me that Jupyter Notebook and Python might be a fantastic way to depict some of the concepts I’m learning. So, here is Part 1 of some of my guitar notes with the help of Jupyter Notebook and Python.

The 12 Keys

I won’t take the time to explain the notes and basic pattern in music as that information can be found all over the internet. The first idea I wanted to construct was a grid of the 12 keys and the notes within each key. My instructor and I have also talked a lot about the relative minor in each major key, so I wanted my graphic to convey that point, too. I put together this code:

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

%matplotlib inline

# make up my list of notes
chromatic_scale_ascending = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B']
# since I usually start on the low E string, rearrange the notes starting on E
scale_from_e = (chromatic_scale_ascending + chromatic_scale_ascending)[4:16]

# the scale pattern:
# root, whole step, whole step, half step, whole step, whole step, whole step, half step
key_steps = [2, 2, 1, 2, 2, 2]  # on the guitar, a whole step is two frets
major_keys = []
for root in scale_from_e:
    three_octaves = scale_from_e * 3
    steps_from_root = three_octaves.index(root)
    major_scale = [root]
    # construct the unique notes in the scale
    for step in key_steps:
        steps_from_root += step
        major_scale.append(three_octaves[steps_from_root])
        
    # span the scale across 3 octaves
    major_keys.append(major_scale * 2 + [root])
    
df_major_keys = pd.DataFrame(major_keys)
df_major_keys.columns = df_major_keys.columns + 1  # start counting notes at 1 instead of 0

# use this function to highlight the relative minor scales in orange
def highlight_natural_minor(data):
    df = data.copy()
    df.iloc[:,:] = 'font-size:20px;height:30px'
    df.iloc[:,5:13] = 'background-color: lightgray; font-size:20px'
    return df

print('The 12 keys and the notes within them:')
df_major_keys.style.apply(highlight_natural_minor, axis=None)

Which produced this handy graphic:

The 12 keys and their notes

For simplicity, I used sharps in my keys instead of flats. The highlighted part of the table marks the relative minor portion of the major key.

The notes of the fret board

Probably one of the best ways to learn the notes on your guitar’s fret board is to trace out the fret board on a blank piece of paper and start filling in each note by hand. Do that a few hundred times and you’ll probably start remembering the notes. Being lazy, though, I wanted to have my computer do that work for me. Here’s the code I came up with to write out the fret board:

standard_tuned_strings = ['E', 'A', 'D', 'G', 'B', 'E']
chromatic_scale_ascending = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B']
col_names = ['Low E', 'A', 'D', 'G', 'B', 'High E']
fretboard_notes = []

for string in standard_tuned_strings:
    start_pos = chromatic_scale_ascending.index(string)
    fretboard_notes.append((chromatic_scale_ascending + chromatic_scale_ascending)[start_pos+1:start_pos+13])

df_fretboard = pd.DataFrame(np.array(fretboard_notes).T, index=np.arange(1, 13), columns=col_names)
df_fretboard.index.name = 'fret'

def highlight_select_frets(data):
    fret_markers = [2, 4, 6, 8, 11]
    df = data.copy()
    df.iloc[:,:] = 'font-size:20px'
    df.iloc[fret_markers,:] = 'background-color: lightgray; font-size:20px'
    return df

df_fretboard.style.apply(highlight_select_frets, axis=None)
Notes on the guitar fret board (1st through 12th fret, standard tuning)

More notes to come, so stay tuned! (Puns intended)

Iterating over a date range

I leverage a number of different programming and scripting tools. Recently, I found myself in a situation where I had to write code to loop through a range of dates to do some operations, by month, in not one, not two…but three different languages: Scala, Python, and Bash. The coding principles are the same across the technologies, but the syntax sure is different.

Here are code examples in four technologies–I threw in PowerShell for good measure–for looping through a range of dates. I loop by month, but these could easily be adapted to loop by day or year or whatever increment fits your needs.

Scala

import java.time.LocalDate
import java.time.format.DateTimeFormatter
import java.util.Date

val start = LocalDate.of(2020, 1, 1) // inclusive in loop
val end = LocalDate.of(2020, 9, 1) // excluded from loop

val template = "This loop is for Year %1$d and Month (zero padded) %2$s \n"

val date_range = Iterator.iterate(start) { _.plusMonths(1) }.takeWhile(_.isBefore(end))
while(date_range.hasNext){
	val d = date_range.next
	val s = template.format(d.getYear, d.format(DateTimeFormatter.ofPattern("MM")))
	print(s)
}

Python

import datetime
import calendar

start = datetime.date(2020, 1, 1)
end = datetime.date(2020, 9, 1)
template = "This loop is for Year {0} and Month (zero padded) {1:%m}"

while start != end:
	s = template.format(start.year, start)
	print(s)
	days_in_month = calendar.monthrange(start.year, start.month)[1]
	start = start + datetime.timedelta(days=days_in_month)
	

Bash

start=2020-1-1
end=2020-9-1

while [ "$start" != "$end" ]; do
	s="`date -d "$start" +"This loop is for Year %Y and Month (zero padded) %m"`"
	echo s
	start=$(date -I -d "$start + 1 month")
done

PowerShell

$start = get-date "2020-1-1"
$end = Get-Date "2020-9-1"

while($start -ne $end){
    "This loop is for Year {0:yyyy} and Month (zero padded) {0:MM}" -f $start
    $start = $start.AddMonths(1)
}

Thinning out your tick labels

Have you ever rendered a chart with Pandas and/or Matplotlib where one or both of your axes (axises?) rendered as a smear of overlapping, unreadable black text?

https://youtu.be/d9kuDizrBPc?t=70
If you can read this, you don’t need glasses

As an example, let’s create a bar chart of COVID-19 data. [As an aside: I’ve noticed that line charts seem to automatically thin out any overlapping tick labels and tend not to fall prey to this problem.]

Load and clean up the data

After downloading the CSV data, I wrote the following code to load the data and prepare it for visualization:

df_covid_confirmed_us = pd.read_csv('./data/time_series_covid19_confirmed_US_20200720.csv')
df_covid_deaths_us = pd.read_csv('./data/time_series_covid19_deaths_US_20200720.csv')

cols_to_keep1 = [i for i, v in enumerate(df_covid_confirmed_us.columns) if v in ['Admin2', 'Province_State'] or v.endswith('20')]
cols_to_keep2 = [i for i, v in enumerate(df_covid_deaths_us.columns) if v in ['Admin2', 'Province_State'] or v.endswith('20')]
df_covid_confirmed_ohio = df_covid_confirmed_us[df_covid_confirmed_us.Province_State=='Ohio'].iloc[:,cols_to_keep1].copy()
df_covid_deaths_ohio = df_covid_deaths_us[df_covid_deaths_us.Province_State=='Ohio'].iloc[:,cols_to_keep2].copy()

df_covid_confirmed_ohio.head()

Tidy up the dataframes

The data is still a bit untidy, so I wrote this additional code to transform it into a more proper format:

date_cols = df_covid_confirmed_ohio.columns.tolist()[2:]
rename_cols_confirmed = {'variable': 'obs_date', 'value': 'confirmed_cases'}
rename_cols_deaths = {'variable': 'obs_date', 'value': 'deaths'}

df_covid_confirmed_ohio = pd.melt(df_covid_confirmed_ohio.reset_index(), id_vars=['Admin2', 'Province_State'], 
                                  value_vars=date_cols).rename(columns=rename_cols_confirmed)
df_covid_deaths_ohio = pd.melt(df_covid_deaths_ohio.reset_index(), id_vars=['Admin2', 'Province_State'], 
                               value_vars=date_cols).rename(columns=rename_cols_deaths)

df_covid_confirmed_ohio['obs_date'] = pd.to_datetime(df_covid_confirmed_ohio.obs_date)
df_covid_deaths_ohio['obs_date'] = pd.to_datetime(df_covid_deaths_ohio.obs_date)

print(df_covid_confirmed_ohio.head())
print(df_covid_deaths_ohio.head())

Concatenate the two dataframes together

I’d like to do a nice, side-by-side comparison, in bar chart form, of these two datasets. One way to do that is to concatenate both dataframes together and then render your chart from the single result. Here’s the code I wrote to concatenate both datasets together:

df_covid_confirmed_ohio['data_type'] = 'confirmed cases'
df_covid_confirmed_ohio['cnt'] = df_covid_confirmed_ohio.confirmed_cases
df_covid_deaths_ohio['data_type'] = 'deaths'
df_covid_deaths_ohio['cnt'] = df_covid_deaths_ohio.deaths
drop_cols = ['confirmed_cases', 'deaths', 'Admin2', 'Province_State']

df_combined_data = pd.concat([df_covid_confirmed_ohio[df_covid_confirmed_ohio.obs_date>='2020-5-1'], 
               df_covid_deaths_ohio[df_covid_deaths_ohio.obs_date>='2020-5-1']], sort=False).drop(columns=drop_cols)

Now, render the chart

Ok, I’m finally ready to create my chart:

fig, ax = plt.subplots(figsize=(12,8))
_ = df_combined_data.groupby(['obs_date', 'data_type']).sum().unstack().plot(kind='bar', ax=ax)

# draws the tick labels at an angle
fig.autofmt_xdate()

title = 'Number of COVID-19 cases/deaths in Ohio: {0:%d %b %Y} - {1:%d %b %Y}'.format(df_combined_data.obs_date.min(), 
                                                                                      df_combined_data.obs_date.max())
_ = ax.set_title(title)
_ = ax.set_xlabel('Date')
_ = ax.set_ylabel('Count')

# clean up the legend
original_legend = [t.get_text() for t in ax.legend().get_texts()]
new_legend = [t.replace('(cnt, ', '').replace(')', '') for t in original_legend]
_ = ax.legend(new_legend)
Wow! Those dates along the X axis are completely unreadable!

The X axis is a mess! Fortunately, there are a variety of ways to fix this problem: I particularly like the approach mentioned in this solution. Basically, I’m going to thin out the labels at a designated frequency. In my solution, I only show every fourth date/label. So, here’s my new code with my label fix highlighted:

fig, ax = plt.subplots(figsize=(12,8))
_ = df_combined_data.groupby(['obs_date', 'data_type']).sum().unstack().plot(kind='bar', ax=ax)

# draws the tick labels at an angle
fig.autofmt_xdate()

title = 'Number of COVID-19 cases/deaths in Ohio: {0:%d %b %Y} - {1:%d %b %Y}'.format(df_combined_data.obs_date.min(), 
                                                                                     df_combined_data.obs_date.max())
_ = ax.set_title(title)
_ = ax.set_xlabel('Date')
_ = ax.set_ylabel('Count')

# clean up the legend
original_legend = [t.get_text() for t in ax.legend().get_texts()]
new_legend = [t.replace('(cnt, ', '').replace(')', '') for t in original_legend]
_ = ax.legend(new_legend)

# tick label fix
tick_labels = [l.get_text().replace(' 00:00:00', '') for l in ax.get_xticklabels()]
new_tick_labels = [''] * len(tick_labels)
new_tick_labels[::4] = tick_labels[::4]
_ = ax.set_xticklabels(new_tick_labels)
Much better!

That X axis is much more readable now thanks to the power of Python list slicing.

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