Several websites

https://techcrunch.com/


https://www.codecademy.com/


https://www.freecodecamp.org/

A tech forum.

A tech forum.

https://slashdot.org/

some python code to plot subplots in python

import matplotlib.pyplot as plt

import numpy as np

# Simple data to display in various forms

x = np.linspace(0, 2 * np.pi, 400)

y = np.sin(x ** 2)

plt.close('all')

# Just a figure and one subplot

f, ax = plt.subplots()

ax.plot(x, y)

ax.set_title('Simple plot')

# Two subplots, the axes array is 1-d

f, axarr = plt.subplots(2, sharex=True)

axarr[0].plot(x, y)

axarr[0].set_title('Sharing X axis')

axarr[1].scatter(x, y)

# Two subplots, unpack the axes array immediately

f, (ax1, ax2) = plt.subplots(1, 2, sharey=True)

ax1.plot(x, y)

ax1.set_title('Sharing Y axis')

ax2.scatter(x, y)

# Three subplots sharing both x/y axes

f, (ax1, ax2, ax3) = plt.subplots(3, sharex=True, sharey=True)

ax1.plot(x, y)

ax1.set_title('Sharing both axes')

ax2.scatter(x, y)

ax3.scatter(x, 2 * y ** 2 - 1, color='r')

# Fine-tune figure; make subplots close to each other and hide x ticks for

# all but bottom plot.

f.subplots_adjust(hspace=0)

plt.setp([a.get_xticklabels() for a in f.axes[:-1]], visible=False)

# row and column sharing

f, ((ax1, ax2), (ax3, ax4)) = plt.subplots(2, 2, sharex='col', sharey='row')

ax1.plot(x, y)

ax1.set_title('Sharing x per column, y per row')

ax2.scatter(x, y)

ax3.scatter(x, 2 * y ** 2 - 1, color='r')

ax4.plot(x, 2 * y ** 2 - 1, color='r')

# Four axes, returned as a 2-d array

Scrapy linux cron job not work, how I make it work

I tried to automate  a scrapy job using cron on linux. But it did not work. I searched and found the solution.
First use "which scrapy " to find where the scrapy is. For my machine the scrapy is:

/home/ubuntu/anaconda2/bin/scrapy

Then in the  shell script, write:

cd /path/to/spider 

nohup  /home/ubuntu/anaconda2/bin/scrapy crawl quotes   >> log.txt &

It resolved the problem. Or can write:

cd /path/to/spider 

PATH=$PATH:/home/ubuntu/anaconda2/bin

export PATH

nohup  /home/ubuntu/anaconda2/bin/scrapy crawl quotes   >> log.txt &

Compare Unix date and time

Compare Unix date and time.

To get Unix time, the command is:

current time:

now=`date +"%T"`

we will get a time like "20:55:01"

now=`date +"%H%M%S"`

we will get a time like "205501"

If we want to compare times, we can not compare the times in the format "%H:%M:%S", we can only compare them in the format "%H%M%S". Otherwise we will get an error Illegal number: 20:59:22

To get Unix date, the command is:

date1=`date +"%m/%d/%Y %H:%M:%S"`

We will get a date in like "5/8/2018 20:55:01"

If we want to get timestamp, we will use:

date2=`date +"%s"`

we will get a unix timestamp.

we can compare dates by its unix timestamp. it seems we can not compare two dates like "5/8/2018 20:55:01".  Otherwise we will get an error: Illegal number: 05/08/2018 20:59:22.

Linux Cron, linux job scheduler

Linux Cron, linux job scheduler

https://www.youtube.com/watch?v=4Icg3MYZZqI


https://awc.com.my/uploadnew/5ffbd639c5e6eccea359cb1453a02bed_Setting%20Up%20Cron%20Job%20Using%20crontab.pdf



to edit a cron file "crontab -e". Then you will run a job indefinitely. 

Summary of SQL questions on leetcode

Summary of SQL questions on leetcode

https://byrony.github.io/summary-of-sql-questions-on-leetcode.html

implement decision tree from scratch using python

implement decision tree from scratch using python:

https://machinelearningmastery.com/implement-decision-tree-algorithm-scratch-python/

This guy has a good blog:

https://machinelearningmastery.com/blog/