In [20]:
import numpy as np
In [21]:
a = np.array([[1,2,3],[4,5,6],[7,8,9]]) # making array
In [22]:
a  # displaying array
Out[22]:
array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])
In [23]:
a[a[:,1] > 2, 1] = 99 # boolean mapping
In [24]:
a # redisplay with new shit
Out[24]:
array([[ 1,  2,  3],
       [ 4, 99,  6],
       [ 7, 99,  9]])
In [17]:
b = np.arange(9).reshape(3,3) # making
In [18]:
b # before
Out[18]:
array([[0, 1, 2],
       [3, 4, 5],
       [6, 7, 8]])
In [28]:
b[b[1,:] > 1, 1] = 47 # waves magic wand
In [29]:
b # after
Out[29]:
array([[ 0, 47,  2],
       [ 3, 47,  5],
       [ 6, 47,  8]])
In [31]:
c = np.arange(0,27,3).reshape(3,3) # make
In [32]:
c # just an oridinary simple array
Out[32]:
array([[ 0,  3,  6],
       [ 9, 12, 15],
       [18, 21, 24]])
In [34]:
c[c[2,:] % 6 == 0, 2] = 111 # abra cadabra
In [35]:
c # wallah
Out[35]:
array([[  0,   3, 111],
       [  9,  12,  15],
       [ 18,  21, 111]])
In [55]:
d = np.arange(0,115,13).reshape(3,3) # making
In [56]:
d # before
Out[56]:
array([[  0,  13,  26],
       [ 39,  52,  65],
       [ 78,  91, 104]])
In [59]:
d[d[:,1] == 52, 1] = 0.0 # some magic
In [75]:
d[d[:,1] == 52, 2] = 0 # more magic
d # after lots of magic
Out[75]:
array([[  0,  13,  26],
       [ 39,   0,  65],
       [ 78,  91, 104]])
In [66]:
e = np.arange(0,9,1).reshape(3,3) # making one more just for kicks
In [67]:
e # I want to see if I can make all the numbers around the center one(4) zeros
Out[67]:
array([[0, 1, 2],
       [3, 4, 5],
       [6, 7, 8]])
In [68]:
e[e[:,:] != 4] = 0 # everything not equal to four, change to zero please.



# pretty please
In [76]:
e # call me the "magic man"

# actually please don't. that's a terrible nickname
Out[76]:
array([[0, 0, 0],
       [0, 4, 0],
       [0, 0, 0]])

array[array[row_for_comparison, column_for_comparison] == value_for_comparison, column_for_assignment] = new_value

^ I refer to this below ^

In [78]:
!date

Fri Sep  6 01:40:10 CDT 2019

Hello there stalker and welcome to

DAY 8

Were you afraid for a second that this one was just going to be code? I wouldn't do that to you. Let me start with a riddle

True or False: a boolean index is a list of all the scariest versions of Lil Wayne's favorite drink.

Actually now that I think about it, that makes a lot of sense.

In programming, a boolean is a kind of data type. Also it's the last name of some guy who did something important at some time or another.

The data type is True or False. Watch.

In [74]:
bool_data_crap = True
other_bool_data_crap = False
"don't trip or you'll fall and get a ",type(bool_data_crap),type(other_bool_data_crap)
Out[74]:
("don't trip or you'll fall and get a ", bool, bool)

Bool is boolean for short. Python hates spelling things out not unlike me.

Up top is the basics in numpy (professionals pronounce it "Num-Pie", but I'm trying to push for "numpeee", it sounds way funnier to say outloud) to make a what is called a boolean index.

I tried to explain this concept a few days ago but I'll try again (more for me, less for you), it's using a condition to map True and False against values in an array and then using that map/index to augment/alter one of those values.

Well it was kind of tough. That jumble of code-looking words just above where I point out that I'm going to refer to it (find it? it's up there ^) was the key to understanding how boolean indexing works and it was provided by DQ as well. I had to change it a little bit but it was the format I tried to follow in all my practice above that.

If you ask me that's confusing as all hell but I'm sure my commenting helps right?

RIGHT??

This is what that's all about: I've been working on the same "mission" on Dataquest for a few days now. This boolean indexing hurts my gourd. What's worse is that I do it correctly every time and I don't incur any errors.

How is that worse? Isn't not getting errors a good thing when you're programming?

Errors are my life blood. If code spits up an output, I understand it less than I do if I have an error. At least I know that I did something wrong and what I did wrong (if it's a well written error, remember, people write the errors too). I didn't understand what I was doing until array labeled as e up there. Seriously.

Also sometimes the Dataquest mission builders write sentences to make me think more coding is involved then necessary.

I'm going to bed now but I want to leave you with an important message.
























Don't drink lean. It's bad for you.