Following from my previous question, it seems that APL performs a scanl in O(n^2) but the compiler is smart enough to optimize for simple primitives. What then is the best strategy to apply \ to non-simple functions? Additionally, there are many cases when the right associativity does affect the result, for example:
{0⌈⍺+⍵} \ 3 ¯4 1 5 ¯1 ¯2 ¯3 2 0 4 ⍝ 3 0 3 5 4 5 5 5 5 5
Which is not the answer I would have expected 3 0 1 6 5 3 0 2 2 6
I stumbled on one possible solution, but don't know if it's the most idiomatic.
s←0 ⋄ ↑{s⊢←0⌈s+⍵}¨ 3 ¯4 1 5 ¯1 ¯2 ¯3 2 0 4
Correctly gives me 3 0 1 6 5 3 0 2 2 6
Related
Is there a good way in q to input somewhat large complicated nested dictionaries which represent/will be converted to json? I'm trying to control the echarts javascript library which basically just renders charts based on json config options. What I'm doing now is:
opt.title.text:"my chart"
opt.xAxis.data:til 100
opt.series.data:100?5
opt.series.type:`line
toClient[opt] /serializes and sends to browser
but is there an obvious way to get rid of the intermediate assignment? Is making a function to take key-path/value pairs and turn them into a dictionary the way to go or is there a better way to go about this?
Or is this something that should be avoided in q, and instead just manually set write q to set specific options and handle the json object map in the javascript client?
Not sure if this is really what you are looking for, but you can create the nested dictionary structure directly if that's what you're after?
q)`title`xAxis`series!(enlist[`text]!enlist"my chart";enlist[`data]!enlist til 100;`data`type!(100?5;`line))
title | (,`text)!,"my chart"
xAxis | (,`data)!,0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 ..
series| `data`type!(0 1 1 3 3 3 2 2 4 1 3 3 1 4 0 4 4 4 2 4 3 3 4 0 4 0 0 1 0..
I have a file with data in 2 columns X and Y. There are some blocks and they are separated by a blank line. I want to join the points (given by their coordenates x and y in the file) in each block using vectors. I'm trying to use these functions:
prev_x = NaN
prev_y = NaN
dx(x) = (x_delta = x-prev_x, prev_x = ($0 > 0 ? x : 1/0), x_delta)
dy(y) = (y_delta = y-prev_y, prev_y = ($0 > 0 ? y : 1/0), y_delta)
which I've taken from Plot lines and vector in graphical gnuplot (first answer). The command to plot would be plot for[i=0:5] 'Field_lines.txt' every :::i::i u (prev_x):(prev_y):(dx($1)):(dy($2)) with vectors. The output is
and the problem is that the point (0,0) is being included even though it's not in the file. I don't think I understand what the functions dx and dy do exactly and how they are being used with the option using (prev_x):(prev_y):(dx($1)):(dy($2)) so an explanation of this would help me a lot to try to fix this.
This is the file:
#1
0 5
0 4
0 3
0.4 2
0.8 1
0.8 1
#2
2 5
2 4
2 3
2 2
2 1
2 0
#3
4 5
4.2 4
4.5 3
4.6 2
4.7 1
4.7 0
#4
7 5
7.2 4
7.5 3
7.9 2
7.9 1
7.9 0
#5
9 5
9 4
9.2 3
9.5 2
9.5 1
9.5 0
#6
11 7
12 6
13 5
13.3 4
13.5 3
13.5 2
13.6 1
14 0
Thanks!
I'm not completely sure, what the real problem is, but I think you cannot rely on the columns in the using statement to be evaluated from left to right, and your check $0 > 0 in the dx and dy some too late in my opinion.
I usually put all the assignments and conditionals in the first column, and that works fine also in your case:
set offsets 1,1,1,1
unset key
prev_x = prev_y = 1
plot for [i=0:5] 'Field_lines.txt' every :::i::i \
u (x_delta = prev_x-$1, prev_x=$1, y_delta=prev_y-$2, prev_y=$2, ($0 == 0 ? 1/0 : prev_x)):(prev_y):(x_delta):(y_delta) with vectors backhead
Also, to draw a vector from j-th row to the point in the following row you must invert the definition of x_delta and use backhead to draw the vectors in the correct direction
The graph consists of more than three million nodes and more than 20 million edges. I'm using igraph package on a 8G RAM linux server. The code is
cliques(g,min=3,max=3)
After six days passed, the code is still running. Is there a better way to find all the triples in a graph?
Following #GaborCsardi suggestion you can see this simple example (I used http://igraph.org/nightly igraph dev version)
kite <- graph.famous("Krackhardt_Kite")
triangles(kite)
which yields:
[1] 4 1 2 4 1 3 4 2 5 4 6 1 4 6 3 4 6 7 4 7 2 4 7 5 6 1 3 6 7 8 7 2 5
for the (undirected) graph "Krackhardt_Kite"
You can compare the results with
plot(kite)
Hope this helps
Here is a problem. I need to find working days between two dates (without weekends). I currently found and was able to successfully use this approach:
SELECT 5 * (DATEDIFF(DateClosed, DateOpened) DIV 7) + MID('0123455501234445012333450122234501101234000123450',
7 * WEEKDAY(DateOpened) + WEEKDAY(DateClosed) + 1, 1) AS TotalResolutionTimeBusinessDays
FROM table1
This is a complex calculation based on a matrix:
| M T W T F S S
-|--------------
M| 0 1 2 3 4 5 5
T| 5 0 1 2 3 4 4
W| 4 5 0 1 2 3 3
T| 3 4 5 0 1 2 2
F| 2 3 4 5 0 1 1
S| 0 1 2 3 4 0 0
S| 0 1 2 3 4 5 0
In the matrix, the intersection of any given x and y value pair (WEEKDAY(#S) and WEEKDAY(#E) yields the difference in work days between the two values. The 49 values in the table are concatenated into the following string: 0123455501234445012333450122234501101234000123450.
This works fine for me but now I need to present difference between dates in another format. E.g.: Let's say we have two dates: StartDate = '2013-06-28 01:27:35' and EndDate = '2013-07-08 16:47:21'. If we use method described above we get 7 working days which is correct. But I need to count all the difference between dates(including hours and minutes) so it could look like
SELECT TIME_TO_SEC(TIMEDIFF('2013-07-08 16:47:21','2013-06-28 01:27:35')) / 3600 / 24
which without weekends should be value like 7.64 days.
Any suggestions how to write a calculation based on that format? Any help would be much appreciated.
I have a txt file which contains a set of 3 Dimensional data points and I would like to create a vtkPolyData based on those points.
In the file, I have the number of points on the first line, in my case they are 6 x 6. And after that the actual coordinates of each point. The content of the file is like this.
6 6
1 1 3
2 1 3.4
3 1 3.6
4 1 3.6
5 1 3.4
6 1 3
1 2 3
2 2 3.8
3 2 4.2
4 2 4.2
5 2 3.8
6 2 3
1 3 3
2 3 3
3 3 3
4 3 3
5 3 3
6 3 3
1 4 3
2 4 3
3 4 3
4 4 3
5 4 3
6 4 3
1 5 3
2 5 3.8
3 5 4.2
4 5 4.2
5 5 3.8
6 5 3
1 6 3
2 6 3.4
3 6 3.6
4 6 3.6
5 6 3.4
6 6 3
How can I build a vtkPolyData structure with a txt file with this data?
It looks to me like you have a regularly gridded series of points, right? If so, vtkImageData might be a better choice. You can always use a geometry filter afterwards to convert to polydata if you really need it that way.
Create a vtkImageData instance.
Set its dimensions to (6, 6, 1) (the third dimension is ignored).
Set its data type to an appropriate type (float or double, I guess).
Call AllocateScalars();
If in C++,
call GetScalarPointer() and cast it to the data type set in 3.
This pointer will point to an array of size 36. You can just fill each point as you would normally.
If in another language (TCL/Python/Java), call SetScalarComponentFromFloat on the image data, with the arguments (x, y, 0, 0, value). The first 0 is the 3rd dimension and the second is for the first component.
This will give you a grid, and it'll be far more memory efficient than a polydata.
If you want to visualize only the points, use a vtkDataSetMapper, and setup the actor's property with SetRepresentationToPoints(), setting an appropriate point size. That will do a simple job of visualization.
Are these examples useful? In particular, this does generation of points and polygons, so it should be possible to adapt. The core seems to be (with lots left out):
# ...
vtkPolyData shell
vtkFloatPoints points
vtkCellArray strips
# Generate points...
loop {
...
points InsertPoint $k $x0 $x1 $x2
}
shell SetPoints points
points Delete
# Generate triangles/polygons...
loop {
strips InsertNextCell $NP2
# ...
strips InsertCellPoint [expr $kb +$ke ]
# ...
strips InsertCellPoint [expr $kb +$ke ]
}
shell SetStrips strips
strips Delete
# ...