I'm doing a nested iteration over two lists, in which I am populating some StringBuffers, like this:
var int_list = [1, 2, 3];
var letters_list = ['a', 'b', 'c'];
var row_strings = List.filled(3, StringBuffer());
var single_buffer = StringBuffer();
int_list.asMap().forEach((int_index, column) {
letters_list.asMap().forEach((letter_index, letter) {
// debug the writing operation
print('writing $letter_index - $letter');
row_strings[letter_index].write(letter);
// try a buffer not in a list as a test
if (letter_index == 0) {
single_buffer.write(letter);
}
});
});
print(single_buffer);
print(row_strings);
What I expect to happen is that in the list of StringBuffers, buffer 0 gets all the 'a's, buffer 1 gets all the 'b's, and buffer 3 the 'c'.
The debug output confirms that the writing operation is doing the right thing:
writing 0 - a
writing 1 - b
writing 2 - c
writing 0 - a
writing 1 - b
writing 2 - c
writing 0 - a
writing 1 - b
writing 2 - c
and the single string buffer gets the right output:
aaa
But the output of the list is this:
[abcabcabc, abcabcabc, abcabcabc]
What is going on here? There seems to be some strange behaviour when the StringBuffers are in a list.
Your problem is this line:
var row_strings = List.filled(3, StringBuffer());
This constructor is documented as:
List.filled(int length, E fill, {bool growable: false})
Creates a list of the given length with fill at each position.
https://api.dart.dev/stable/2.10.5/dart-core/List/List.filled.html
So what you are doing is creating a single StringBuffer instance and uses that on every position in your row_strings list.
What you properly want, is to create a new StringBuffer for each position in the list. You need to use List.generate for that:
List.generate(int length,E generator(int index), {bool growable: true})
Generates a list of values.
Creates a list with length positions and fills it with values created by calling generator for each index in the range 0 .. length - 1 in increasing order.
https://api.dart.dev/stable/2.10.5/dart-core/List/List.generate.html
Using that, we end up with:
final row_strings = List.generate(3, (_) => StringBuffer());
We don't need the index argument in our generator so I have just called it _. The function (_) => StringBuffer() will be executed for each position in the list and saved. Since out function returns a new instance of StringBuffer each time it is executed, we will end up with a list of 3 separate StringBuffer instances.
I have a Data object in swift that is an array of Int16 objects. For some reason using ".pcmFormatInt16" did not work for the format of my AVAudioPCMBuffer and yielded no sound, or a memory error. Eventually, I was able to get white noise/static to play from the speakers by converting the Int16 to a float and putting that onto both channels of my AVAudioPCMBuffer. I have a feeling that I am getting close to the answer, because whenever I speak into the microphone I hear a different frequency of static. I think the issue is that I am not converting the converted Int16 into the buffer floatChannelData.
Here is my code:
for ch in 0..<2 {
for i in 0..<audio.count {
var val = Float( Int16(audio[i]) ) / Float(Int16.max)
if( val > 1 ){
val = 1;
}
if( val < -1 ){
val = -1;
}
self.buffer.floatChannelData![ch][i+self.bufferCount] = val
self.bufferCount+=1
}
}
self.audioFilePlayer.scheduleBuffer(self.buffer, at:nil, options: .interruptsAtLoop, completionHandler: {
print("played sum")
self.bufferCount=0
})
a typical multi-channel PCM buffer has the channels interleaving on a per sample basis although, not being familiar with swift audio, I find it refreshing to see here channels given a dimension on the buffer datastructure
... a flag goes up when I see your guard checks clamping val > 1 set to val = 1 etc. ... elsewhere that is not needed as those boundary checks are moot as the data nicely falls into place as is
... my guess is your input audio[] is signed int 16 because of your val > 1 and val < -1 ? if true then dividing by max int float is wrong as you would be loosing half your dynamic range ...
I suggest you look closely at your
var val = Float( Int16(audio[i]) ) / Float(Int16.max)
lets examine range of your ints in audio[]
2^16 == 65536 // if unsigned then values range from 0 to (2^16 - 1) which is 0 to 65535
2^15 == 32768 // if signed then values would range from -32768 to (2^15 - 1) which is -32768 to 32767
Please tell is whether input buffer audio[] is signed or not ... sometimes its helpful to identify the max_seen and min_seen values of your input data ... do this and tell us the value of max and min of your input audio[]
Now lets focus on your desired output buffer self.buffer.floatChannelData ... since you are saying its 16 bit float ... what is the valid range here ? -1 < valid_value < 1 ?
We can continue once you tell us answers to these basic questions
This question already has answers here:
Why does Lua's length (#) operator return unexpected values?
(2 answers)
Closed 6 years ago.
I am new to lua and my lua version is 5.1.
I've got this problem. Can anybody help me to explain '#'?
local tblTest =
{
[1] = 2,
[2] = 5,
[5] = 10,
}
print(#tblTest)
this output 2 and ..
local tblTest =
{
[1] = 2,
[2] = 5,
[4] = 10,
}
print(#tblTest)
output is 4. Why?
thanks all of u.
The output is 4 because the last key with a value is 4 but that doesn't mean that 3 isn't also defined. In lua 3 would be defined as nil. So when you use the # operator it counts every key in a sequence with a value until the last non-nil value. Except,(and I could be wrong about this) the last key in the table is a power of 2, which do to language optimization, it counts up to the value that is a power of 2. In general you should stay away from tables with nil values as there are some other weird behaviors that happen because of this.
This chunk with do what you want though:
local T = {
[1] = 2,
[2] = 5,
[10] = 10
}
local lengthNum = 0
For k, v in pairs(T) do -- for every key in the table with a corresponding non-nil value
lengthNum = lengthNum + 1
end
print(lengthNum)
}
What this does is it checks the entire table for keys (such as [1] or [2]) and checks if they have value. Every key with a non-nil value runs the for loop one more time. There might be a shorter way to this, but this is how I would do it.
I've run into an issue with the TabularAdapter in the TraitsUI package...
I've been trying to figure this out on my own for much too long now, so I wanted to ask the experts here for some friendly advise :)
I'm going to add a piece of my program that illustrates my problem(s), and I'm hoping someone can look it over and say 'Ah Ha!...Here's your problem' (my fingers are crossed).
Basically, I can use the TabularAdapter to produce a table editor into an array of dtypes, and it works just fine except:
1) whenever I change the # of elements (identified as 'Number of fractures:'), the array gets resized, but the table doesn't reflect the change until after I click on one of the elements. What I'd like to happen is that the # of rows (fractures) changes after I release the # of fractures slider. Is this doable?
2) The second issue I have is that if the array gets resized before it's displayed by .configure_traits() (by the notifier when Number_of_fractures gets modified), I can shrink the size of the array, but I can't increase it over the new size.
2b) I thought I'd found a way to have the table editor display the full array even when it's increased over the 5 set in the code (just before calling .trait_configure()), but I was fooled :( I tried adding another Group() in front of the vertical_fracture_group so the table wasn't the first thing to display. This more closely emulates my entire program. When I did this, I was locked into the new smaller size of the array, and I could no longer increase its size to my maximum of 15. I'm modifying the code to reflect this issue.
Here's my sample code:
# -*- coding: utf-8 -*-
"""
This is a first shot at developing a ****** User Interface using Canopy by
Enthought. Canopy is a distribution of the Python language which has a lot of
scientific and engineering features 'built-in'.
"""
#-- Imports --------------------------------------------------------------------
from traitsui.api import TabularEditor
from traitsui.tabular_adapter import TabularAdapter
from numpy import zeros, dtype
from traits.api import HasTraits, Range
from traitsui.api import View, Group, Item
#-- FileDialogDemo Class -------------------------------------------------------
max_cracks = 15 #maximum number of Fracs/cracks to allow
class VertFractureAdapter(TabularAdapter):
columns = [('Frac #',0), ('X Cen',1), ('Y Cen',2), ('Z Cen',3),
('Horiz',4), ('Vert',5), ('Angle',6)]
class SetupDialog ( HasTraits ):
Number_Of_Fractures = Range(1, max_cracks) # line 277
vertical_frac_dtype = dtype([('Fracture', 'int'), ('x', 'float'), ('y', 'float'),
('z', 'float'), ('Horiz Length', 'float'), ('Vert Length', 'float')
, ('z-axis Rotation, degrees', 'float')])
vertical_frac_array = zeros((max_cracks), dtype=vertical_frac_dtype)
vertical_fracture_group = Group(
Item(name = 'vertical_frac_array',
show_label = False,
editor = TabularEditor(adapter = VertFractureAdapter()),
width = 0.5,
height = 0.5,
)
)
#-- THIS is the actual 'View' that gets put on the screen
view = View(
#Note: When as this group 'displays' before the one with the Table, I'm 'locked' into my new maximum table display size of 8 (not my original/desired maximum of 15)
Group(
Item( name = 'Number_Of_Fractures'),
),
#Note: If I place this Group() first, my table is free to grow to it's maximum of 15
Group(
Item( name = 'Number_Of_Fractures'),
vertical_fracture_group,
),
width = 0.60,
height = 0.50,
title = '****** Setup',
resizable=True,
)
#-- Traits Event Handlers --------------------------------------------------
def _Number_Of_Fractures_changed(self):
""" Handles resizing arrays if/when the number of Fractures is changed"""
print "I've changed the # of Fractures to " + repr(self.Number_Of_Fractures)
#if not self.user_StartingUp:
self.vertical_frac_array.resize(self.Number_Of_Fractures, refcheck=False)
for crk in range(self.Number_Of_Fractures):
self.vertical_frac_array[crk]['Fracture'] = crk+1
self.vertical_frac_array[crk]['x'] = crk
self.vertical_frac_array[crk]['y'] = crk
self.vertical_frac_array[crk]['z'] = crk
# Run the program (if invoked from the command line):
if __name__ == '__main__':
# Create the dialog:
fileDialog = SetupDialog()
fileDialog.configure_traits()
fileDialog.Number_Of_Fractures = 8
In my discussion with Chris below, he made some suggestions that so far haven't worked for me :( Following is my 'current' version of this test code so Chris (or anyone else who wishes to chime in) can see if I'm making some glaring error.
# -*- coding: utf-8 -*-
"""
This is a first shot at developing a ****** User Interface using Canopy by
Enthought. Canopy is a distribution of the Python language which has a lot of
scientific and engineering features 'built-in'.
"""
#-- Imports --------------------------------------------------------------------
from traitsui.api import TabularEditor
from traitsui.tabular_adapter import TabularAdapter
from numpy import zeros, dtype
from traits.api import HasTraits, Range, Array, List
from traitsui.api import View, Group, Item
#-- FileDialogDemo Class -------------------------------------------------------
max_cracks = 15 #maximum number of Fracs/cracks to allow
class VertFractureAdapter(TabularAdapter):
columns = [('Frac #',0), ('X Cen',1), ('Y Cen',2), ('Z Cen',3),
('Horiz',4), ('Vert',5), ('Angle',6)]
even_bg_color = 0xf4f4f4 # very light gray
class SetupDialog ( HasTraits ):
Number_Of_Fractures = Range(1, max_cracks) # line 277
dummy = Range(1, max_cracks)
vertical_frac_dtype = dtype([('Fracture', 'int'), ('x', 'float'), ('y', 'float'),
('z', 'float'), ('Horiz Length', 'float'), ('Vert Length', 'float')
, ('z-axis Rotation, degrees', 'float')])
vertical_frac_array = Array(dtype=vertical_frac_dtype)
vertical_fracture_group = Group(
Item(name = 'vertical_frac_array',
show_label = False,
editor = TabularEditor(adapter = VertFractureAdapter()),
width = 0.5,
height = 0.5,
)
)
#-- THIS is the actual 'View' that gets put on the screen
view = View(
Group(
Item( name = 'dummy'),
),
Group(
Item( name = 'Number_Of_Fractures'),
vertical_fracture_group,
),
width = 0.60,
height = 0.50,
title = '****** Setup',
resizable=True,
)
#-- Traits Event Handlers --------------------------------------------------
def _Number_Of_Fractures_changed(self, old, new):
""" Handles resizing arrays if/when the number of Fractures is changed"""
print "I've changed the # of Fractures to " + repr(self.Number_Of_Fractures)
vfa = self.vertical_frac_array
vfa.resize(self.Number_Of_Fractures, refcheck=False)
for crk in range(self.Number_Of_Fractures):
vfa[crk]['Fracture'] = crk+1
vfa[crk]['x'] = crk
vfa[crk]['y'] = crk
vfa[crk]['z'] = crk
self.vertical_frac_array = vfa
# Run the program (if invoked from the command line):
if __name__ == '__main__':
# Create the dialog:
fileDialog = SetupDialog()
# put the actual dialog up...if I put it up 'first' and then resize the array, I seem to get my full range back :)
fileDialog.configure_traits()
#fileDialog.Number_Of_Fractures = 8
There are two details of the code that are causing the problems you describe. First, vertical_frac_array is not a trait, so the tabular editor cannot monitor it for changes. Hence, the table only refreshes when you manually interact with it. Second, traits does not monitor the contents of an array for changes, but rather the identity of the array. So, resizing and assigning values into the array will not be detected.
One way to fix this is to first make vertical_frac_array and Array trait. E.g. vertical_frac_array = Array(dtype=vertical_frac_dtype). Then, inside of _Number_Of_Fractures_changed, do not resize the vertical_frac_array and modify it in-place. Instead, copy vertical_frac_array, resize it, modify the contents, and then reassign the manipulated copy back to vertical_frac_array. This way the table will see that the identity of the array has changed and will refresh the view.
Another option is to make vertical_frac_array a List instead of an Array. This avoids the copy-and-reassign trick above because traits does monitor the content of lists.
Edit
My solution is below. Instead of resizing the vertical_frac_array whenever Number_Of_Fractures changes, I instead recreate the array. I also provide a default value for vertical_frac_array via the _vertical_frac_array_default method. (I removed from unnecessary code in the view as well.)
# -*- coding: utf-8 -*-
"""
This is a first shot at developing a ****** User Interface using Canopy by
Enthought. Canopy is a distribution of the Python language which has a lot of
scientific and engineering features 'built-in'.
"""
#-- Imports --------------------------------------------------------------------
from traitsui.api import TabularEditor
from traitsui.tabular_adapter import TabularAdapter
from numpy import dtype, zeros
from traits.api import HasTraits, Range, Array
from traitsui.api import View, Item
#-- FileDialogDemo Class -------------------------------------------------------
max_cracks = 15 #maximum number of Fracs/cracks to allow
vertical_frac_dtype = dtype([('Fracture', 'int'), ('x', 'float'), ('y', 'float'),
('z', 'float'), ('Horiz Length', 'float'), ('Vert Length', 'float')
, ('z-axis Rotation, degrees', 'float')])
class VertFractureAdapter(TabularAdapter):
columns = [('Frac #',0), ('X Cen',1), ('Y Cen',2), ('Z Cen',3),
('Horiz',4), ('Vert',5), ('Angle',6)]
class SetupDialog ( HasTraits ):
Number_Of_Fractures = Range(1, max_cracks) # line 277
vertical_frac_array = Array(dtype=vertical_frac_dtype)
view = View(
Item('Number_Of_Fractures'),
Item(
'vertical_frac_array',
show_label=False,
editor=TabularEditor(
adapter=VertFractureAdapter(),
),
width=0.5,
height=0.5,
),
width=0.60,
height=0.50,
title='****** Setup',
resizable=True,
)
#-- Traits Defaults -------------------------------------------------------
def _vertical_frac_array_default(self):
""" Creates the default value of the `vertical_frac_array`. """
return self._calculate_frac_array()
#-- Traits Event Handlers -------------------------------------------------
def _Number_Of_Fractures_changed(self):
""" Update `vertical_frac_array` when `Number_Of_Fractures` changes """
print "I've changed the # of Fractures to " + repr(self.Number_Of_Fractures)
#if not self.user_StartingUp:
self.vertical_frac_array = self._calculate_frac_array()
#-- Private Interface -----------------------------------------------------
def _calculate_frac_array(self):
arr = zeros(self.Number_Of_Fractures, dtype=vertical_frac_dtype)
for crk in range(self.Number_Of_Fractures):
arr[crk]['Fracture'] = crk+1
arr[crk]['x'] = crk
arr[crk]['y'] = crk
arr[crk]['z'] = crk
return arr
# Run the program (if invoked from the command line):
if __name__ == '__main__':
# Create the dialog:
fileDialog = SetupDialog()
fileDialog.configure_traits()
I am a student in high school and I am currently learning in Delphi XE3. We are learning about BIT manipulation. We have an assignment and while I have read a lot on the subject and understand the entire process of storing information in Bits and SHL/SHR I am having difficulty understanding how to do this process in Delphi.
The assignment is as follows:
Decimal Hexidecimal Binary
1 0x0001 0000000000000001
2 0x0002 0000000000000010
4 0x0004 0000000000000100
Passing an integer value in an XML file to identify the options set. For example. If I wanted to send option 1 and option 2, I would add 1+2=3. I would send 3 as the number to specify that options 1 and 2 are true.
On the client the binary value would be 0000000000000011 = 3
From what I have read I need to use a mask but I do not understand how to do this. How would do I use masks in Delphi ot obtain the individual values which would be True or False.
I tried doing this in a regular Integer variable but it always gets treated as an Integer and the result is very strange. If I convert the integer to a binary string representation and I iterate thru the characters the result is correct but I am assuming that I should not be doing this with strings. Any help or an example would be greatly appreciated. Thank you.
You usually check if a particular bit is set in a Integer variable using the and binary operator, and you set individual bits using the or operator, like this:
const
OPTION_X = $01;
OPTION_Y = $02;
OPTION_Z = $04;
var
Options: Byte;
begin
Options := OPTION_X or OPTION_Y; //actually 3, like in your example
//check if option_X is set
if (Options and OPTION_X) = OPTION_X then
ShowMessage('Option X is set'); //this message is shown, because the bit is set
//check if option_Z is set
if (Options and OPTION_Z) = OPTION_Z then
ShowMessage('Option Z is set'); //this message is NOT shown
end;
The different OPTION_ constants, are actually masks, in the sense they are used to mask bits to zero (to check if a particular bit is set) or to mask bits to 1 (to set a particular bit).
Consider this fragment:
begin
..
if cbOptionX.Checked then
Options := Options or OPTION_X;
..
the or will mask the first bit to 1. If we start with a Options value (in binary) of 01010000, the resulting Options would be 01010001
01010000
OR 00000001 //OPTION_X
= 01010001
the same value is used to mask all the other bits to 0 to check if a particular bit is set. The if condition, for example: (Options and OPTION_Z) = OPTION_Z, does this:
first it MASKS all the non-interesting bytes of the Option variable to 0. If we consider the last value of 01010001, the operation will result in clearing all the bits, but the first.
01010001
AND 00000001
= 00000001
considering a starting value of 01010000 it will return zero:
01010000
AND 00000001
= 00000000
next, it compares if that value is equal to the mask itself. If it is equal, the bit was set in the original Options variable, otherwise it was not set. If your mask contains only one bit, that's matter of taste, you can just check if the resulting value is, for example, different than 0, but if your mask contains multiple bits and you want to check if all the bits was set, you have to check for equality.
Delphi has a predefined type TIntegerSet which allows to use set operators. Assuming that options is an Integer, you can check if any bit (0-based) is set like this:
option1 := 0 in TIntegerSet(options); { Bit 0 is set? }
option3 := 2 in TIntegerSet(options); { Bit 2 is set? }
Changing the options is done via Include or Exclude:
Include(TIntegerSet(options), 0); { set bit 0 }
Exclude(TIntegerSet(options), 2); { reset bit 2 }
Of course you can use any other set operator that may be helpful.
Delphi has Bitwise Operators for manipulating individual bits of integer types. Look at the shl, shr, and, or, and xor operators. To combine bits, use the or operator. To test for bits, use the and operator. For example, assuming these constants:
const
Option1 = 0x0001;
Option2 = 0x0002;
Option3 = 0x0004;
The or operator looks at the bits of both input values and produces an output value that has a 1 bit in places where either input value has a 1 bit. So combining bits would look like this:
var
Value: Integer;
begin
Value := Option1 or Option2;
{
00000000000000000000000000000001 Option1
00000000000000000000000000000010 Option2
-------------------------------- OR
00000000000000000000000000000011 Result
}
...
end;
The and operator looks at the bits of both input values and produces an output value that has a 1 bit only in places where both input value have a 1 bit, otherwise it produces a 0 bit instead. So testing for bits would look like this:
var
Value: Integer;
Option1Set: Boolean;
Option2Set: Boolean;
Option3Set: Boolean;
begin
Value := 7; // Option1 or Option2 or Option3
Option1Set := (Value and Option1) = Option1;
{
00000000000000000000000000000111 Value
00000000000000000000000000000001 Option1
-------------------------------- AND
00000000000000000000000000000001 Result
}
Option2Set := (Value and Option2) = Option2;
{
00000000000000000000000000000111 Value
00000000000000000000000000000010 Option2
-------------------------------- AND
00000000000000000000000000000010 Result
}
Option3Set := (Value and Option3) = Option3;
{
00000000000000000000000000000111 Value
00000000000000000000000000000100 Option3
-------------------------------- AND
00000000000000000000000000000100 Result
}
...
end;