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  • parsing a list and producing a structure of that

    - by qzar
    ;; structure representing homework points ;; nr: number - the number of the homework ;; points: number - the number of points reached (define-struct homework (nr points)) ;; parse-homework: (list of number pairs) -> (list of homework) ;; The procedure takes a list of number pairs and produces a list of homework structures ;; Example: (parse-homework (list (list 1 6) (list 2 7) (list 3 0))) should produce (list (make-homework 1 6) (make-homework 2 7) (make-homework 3 0)) (define (parse-homework homework-entries) (if (and (= (length (first homework-entries) 2))(= (length (parse-homework (rest homework-entries)) 2))) (make-homework (first homework-entries) (parse-homework (rest homework-entries))) (error 'Non-valid-input "entered list is not of length two")) ) (parse-homework (list (list 1 6) (list 2 7) (list 3 0))) This code produces the error length: expects 1 argument, given 2: (list 1 6) 2 I really appreciate every explanation that you can give me to get in in this scheme-stuff... Thank you very much

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  • Any simple shape recognition libraries for Java?

    - by Phil
    I am working on a on-screen keyboard for Android, and I need to recognize starting points, turning points and end points of lines drawn by the user on the keyboard. A simple straightening function would be nice, as it is difficult to draw a perfectly straight line even with a stylus, not to mention finger-only touchscreens today. What I am trying to write is something like Swype. Any good libraries that I can use or make reference to?

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  • Metric 3d reconstruction

    - by srand
    I'm trying to reconstruct 3D points from 2D image correspondences. My camera is calibrated. The test images are of a checkered cube and correspondences are hand picked. Radial distortion is removed. After triangulation the construction seems to be wrong however. The X and Y values seem to be correct, but the Z values are about the same and do not differentiate along the cube. The 3D points look like as if the points were flattened along the Z-axis. What is going wrong in the Z values? Do the points need to be normalized or changed from image coordinates at any point, say before the fundamental matrix is computed? (If this is too vague I can explain my general process or elaborate on parts)

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  • excel vba moving non-contiguous range selection to an array

    - by Russ Urquhart
    In the situation where the user select two non-contiguous column ranges i wrote the following: Dim count long Dim points variant Dim i long Set user_range = ActiveWindow.RangeSelection count = user_range.count / 2 ReDim points(1 To count, 1 To 2) For i = 1 To count MsgBox "value is" & user_range.Areas.Item(1).Value(i,1) points(i, 1) = user_range.Areas.Item(1).Value(i,1) points(i, 2) = user_range.Areas.Item(2).Value(i,1) Next i But i get an object error when i try this. Am i indexing Value wrong? This should work right? Is there an easier way to do this? Any help is greatly appreciated! Thanks, Russ

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  • High density Silverlight charting control

    - by ahosie
    I've been looking into Silverlight charting controls to display a large number of samples, (~10,000 data points in five separate series - ~50k points all up). I have found the existing options produced by Dundas, Visifire, Microsoft etc to be extremely poor performers when displaying more than a few hundred data points. I believe the performance issues with existing chart controls is caused by the heavy use of vector graphics. Ergo one solution would be a client-side chart control that uses the WritableBitmap class to generate a raster chart. Before I fall too far down the wheel re-invention rabbit hole - has anyone found a third party or OSS control that will manage large numbers of data points on a sparkline?

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  • Interpolation of scattered data: What could I do?

    - by Simon
    Hi! I need your help. I'm working on a 3D chart in Java using Java 3D. It should be able to display a bunch of measured values. As measured, the data I get is scattered. This means I will have to interpolate the missing points in order to get my surface plotted nicely. I didn't study all that 3D-Geometry stuff yet and I don't know where to start. My idea is to triangulate the points to a surface and then, based on the triangulation, interpolate the missing points. (see this to have a rough idea of what I want to achieve) Does someone have experiences with the interpolation of scattered data? Is my approach the right one? If yes, what kind of data structures and algorithms will I need in order to triangulate my points cloud?

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  • Fast JSON serialization (and comparison with Pickle) for cluster computing in Python?

    - by user248237
    I have a set of data points, each described by a dictionary. The processing of each data point is independent and I submit each one as a separate job to a cluster. Each data point has a unique name, and my cluster submission wrapper simply calls a script that takes a data point's name and a file describing all the data points. That script then accesses the data point from the file and performs the computation. Since each job has to load the set of all points only to retrieve the point to be run, I wanted to optimize this step by serializing the file describing the set of points into an easily retrievable format. I tried using JSONpickle, using the following method, to serialize a dictionary describing all the data points to file: def json_serialize(obj, filename, use_jsonpickle=True): f = open(filename, 'w') if use_jsonpickle: import jsonpickle json_obj = jsonpickle.encode(obj) f.write(json_obj) else: simplejson.dump(obj, f, indent=1) f.close() The dictionary contains very simple objects (lists, strings, floats, etc.) and has a total of 54,000 keys. The json file is ~20 Megabytes in size. It takes ~20 seconds to load this file into memory, which seems very slow to me. I switched to using pickle with the same exact object, and found that it generates a file that's about 7.8 megabytes in size, and can be loaded in ~1-2 seconds. This is a significant improvement, but it still seems like loading of a small object (less than 100,000 entries) should be faster. Aside from that, pickle is not human readable, which was the big advantage of JSON for me. Is there a way to use JSON to get similar or better speed ups? If not, do you have other ideas on structuring this? (Is the right solution to simply "slice" the file describing each event into a separate file and pass that on to the script that runs a data point in a cluster job? It seems like that could lead to a proliferation of files). thanks.

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  • Finding intersection of two spheres

    - by Onkar Deshpande
    Hi, Consider the following problem - I am given 2 links of length L0 and L1. P0 is the point that the first link starts at and P1 is the point that I want the end of second link to be at in 3-D space. I am supposed to write a function that should take in these 3-D points (P0 and P1) as inputs and should find all configurations of the links that put the second link's end point at P1. My understanding of how to go about it is - Each link L0 and L1 will create a sphere S0 and S1 around itself. I should find out the intersection of those two spheres (which will be a circle) and print all points that are on the circumference of that circle. I saw gmatt's first reply on the http://stackoverflow.com/questions/1406375/finding-intersection-points-between-3-spheres but could not understand it properly since the images did not show up. I also saw a formula for finding out the intersection at mathworld[dot]wolfram[dot]com/Sphere-SphereIntersection[dot]html . I could find the radius of intersection by the method given on mathworld. Also I can find the center of that circle and then use the parametric equation of circle to find the points. The only doubt that I have is will this method work for the points P0 and P1 mentioned above ? Please comment and let me know your thoughts.

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  • Is release without prior retain dangerous?

    - by BankStrong
    I have some code which I think has extra release statements. Is the code incorrect? What is the end result? I don't understand memory management well yet - even after reading lots of articles and stackoverflow answers. Thanks for straightening me out. NSMutableArray *points = [NSMutableArray new]; for (Segment *s in currentWorkout.segments) { [points addObjectsFromArray:[s.track locationPoints]]; } [routeMap update:points]; [points release];

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  • how to read specific number of floats from file in python?

    - by sahel
    I am reading a text file from the web. The file starts with some header lines containing the number of data points, followed the actual vertices (3 coordinates each). The file looks like: # comment HEADER TEXT POINTS 6 float 1.1 2.2 3.3 4.4 5.5 6.6 7.7 8.8 9.9 1.1 2.2 3.3 4.4 5.5 6.6 7.7 8.8 9.9 POLYGONS the line starting with the word POINTS contains the number of vertices (in this case we have 3 vertices per line, but that could change) This is how I am reading it right now: ur=urlopen("http://.../file.dat") j=0 contents = [] while 1: line = ur.readline() if not line: break else: line=line.lower() if 'points' in line : myline=line.strip() word=myline.split() node_number=int(word[1]) node_type=word[2] while 'polygons' not in line : line = ur.readline() line=line.lower() myline=line.split() i=0 while(i<len(myline)): contents[j]=float(myline[i]) i=i+1 j=j+1 How can I read a specified number of floats instead of reading line by line as strings and converting to floating numbers? Instead of ur.readline() I want to read the specified number of elements in the file Any suggestion is welcome..

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  • How can I subsample data from a time series with LINQ to SQL?

    - by Chris Farmer
    I have a database table full of time points and experimental values at those time points. I need to retrieve the values for an experiment and create a thumbnail image showing an XY plot of its data. Because the actual data set for each experiment is potentially 100,000 data points and my image is only 100 pixels wide, I want to sample the data before creating the image. My current query (which retrieves all the data without sampling) is something simple like this: var points = from p in db.DataPoints where p.ExperimentId == myExperimentId orderby p.Time select new { X = p.Time, Y = p.Value } So, how can I best take every nth point from my result set in a LINQ to SQL query?

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  • How to Extract Properties for Refactoring

    - by Ngu Soon Hui
    I have this property public List<PointK> LineList {get;set;} Where PointK consists of the following structure: string Mark{get;set;} double X{get;set;} doible Y{get;set;} Now, I have the following code: private static Dictionary<string , double > GetY(List<PointK> points) { var invertedDictResult = new Dictionary<string, double>(); foreach (var point in points) { if (!invertedDictResult.ContainsKey(point.Mark)) { invertedDictResult.Add(point .Mark, Math.Round(point.Y, 4)); } } return invertedDictResult; } private static Dictionary<string , double > GetX(List<PointK> points) { var invertedDictResult = new Dictionary<string, double>(); foreach (var point in points) { if (!invertedDictResult.ContainsKey(point.Mark)) { invertedDictResult.Add(point .Mark, Math.Round(point.X, 4)); } } return invertedDictResult; } How to restructure the above code?

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  • Confused about definition of a 'median' when constructing a kd-Tree

    - by user352636
    Hi there. Im trying to build a kd-tree for searching through a set of points, but am getting confused about the use of 'median' in the wikipedia article. For ease of use, the wikipedia article states the pseudo-code of kd-tree construction as: function kdtree (list of points pointList, int depth) { if pointList is empty return nil; else { // Select axis based on depth so that axis cycles through all valid values var int axis := depth mod k; // Sort point list and choose median as pivot element select median by axis from pointList; // Create node and construct subtrees var tree_node node; node.location := median; node.leftChild := kdtree(points in pointList before median, depth+1); node.rightChild := kdtree(points in pointList after median, depth+1); return node; } } I'm getting confused about the "select median..." line, simply because I'm not quite sure what is the 'right' way to apply a median here. As far as I know, the median of an odd-sized (sorted) list of numbers is the middle element (aka, for a list of 5 things, element number 3, or index 2 in a standard zero-based array), and the median of an even-sized array is the sum of the two 'middle' elements divided by two (aka, for a list of 6 things, the median is the sum of elements 3 and 4 - or 2 and 3, if zero-indexed - divided by 2.). However, surely that definition does not work here as we are working with a distinct set of points? How then does one choose the correct median for an even-sized list of numbers, especially for a length 2 list? I appreciate any and all help, thanks! -Stephen

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  • Automatic annotation for matlab plot?

    - by Tim
    Hi I have quite a few points plotted in a figure. I am now using annotation() function to add annotation in the same way for these points based on their locations. See my previous question. However they tend to mess up where the points are close to each other. Is there some function available to position the annotations as apart as possible? Thanks and regards!

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  • How to stop OpenGL from applying blending to certain content? (see pics)

    - by RexOnRoids
    Supporting Info: I use cocos2d to draw a sprite (graph background) on the screen (z:-1). I then use cocos2d to draw lines/points (z:0) on top of the background -- and make some calls to OpenGL blending functions before the drawing to SMOOTH out the lines. Problem: The problem is that: aside from producing smooth lines/points, calling these OpenGL blending functions seems to "degrade" the underlying sprite (graph background). As you can see from the images below, the "degraded" background seems to be made darker and less sharp in Case 2. So there is a tradeoff: I can either have (Case 1) a nice background and choppy lines/points, or I can have (Case 2) nice smooth lines/points and a degraded background. But obviously I need both. THE QUESTION: How do I set OpenGL so as to only apply the blending to the layer with the Lines/Points in it and thus leave the background alone? The Code: I have included code of the draw() method of the CCLayer for both cases explained above. As you can see, the code producing the difference between Case 1 and Case 2 seems to be 1 or 2 lines involving OpenGL Blending. Case 1 -- MainScene.h (CCLayer): -(void)draw{ int lastPointX = 0; int lastPointY = 0; GLfloat colorMAX = 255.0f; GLfloat valR; GLfloat valG; GLfloat valB; if([self.myGraphManager ready]){ valR = (255.0f/colorMAX)*1.0f; valG = (255.0f/colorMAX)*1.0f; valB = (255.0f/colorMAX)*1.0f; NSEnumerator *enumerator = [[self.myGraphManager.currentCanvas graphPoints] objectEnumerator]; GraphPoint* object; while ((object = [enumerator nextObject])) { if(object.filled){ /*Commenting out the following two lines induces a problem of making it impossible to have smooth lines/points, but has merit in that it does not degrade the background sprite.*/ //glEnable (GL_BLEND); //glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); glHint (GL_LINE_SMOOTH_HINT, GL_DONT_CARE); glEnable (GL_LINE_SMOOTH); glLineWidth(1.5f); glColor4f(valR, valG, valB, 1.0); ccDrawLine(ccp(lastPointX, lastPointY), ccp(object.position.x, object.position.y)); lastPointX = object.position.x; lastPointY = object.position.y; glPointSize(3.0f); glEnable(GL_POINT_SMOOTH); glHint(GL_POINT_SMOOTH_HINT, GL_NICEST); ccDrawPoint(ccp(lastPointX, lastPointY)); } } } } Case 2 -- MainScene.h (CCLayer): -(void)draw{ int lastPointX = 0; int lastPointY = 0; GLfloat colorMAX = 255.0f; GLfloat valR; GLfloat valG; GLfloat valB; if([self.myGraphManager ready]){ valR = (255.0f/colorMAX)*1.0f; valG = (255.0f/colorMAX)*1.0f; valB = (255.0f/colorMAX)*1.0f; NSEnumerator *enumerator = [[self.myGraphManager.currentCanvas graphPoints] objectEnumerator]; GraphPoint* object; while ((object = [enumerator nextObject])) { if(object.filled){ /*Enabling the following two lines gives nice smooth lines/points, but has a problem in that it degrades the background sprite.*/ glEnable (GL_BLEND); glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); glHint (GL_LINE_SMOOTH_HINT, GL_DONT_CARE); glEnable (GL_LINE_SMOOTH); glLineWidth(1.5f); glColor4f(valR, valG, valB, 1.0); ccDrawLine(ccp(lastPointX, lastPointY), ccp(object.position.x, object.position.y)); lastPointX = object.position.x; lastPointY = object.position.y; glPointSize(3.0f); glEnable(GL_POINT_SMOOTH); glHint(GL_POINT_SMOOTH_HINT, GL_NICEST); ccDrawPoint(ccp(lastPointX, lastPointY)); } } } }

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  • iphone quartz drawing 2 lines on top of each other causes worm effect

    - by Leonard
    I'm using Quartz-2D for iPhone to display a route on a map. The route is colored according to temperature. Because some streets are colored yellow, I am using a slightly thicker black line under the route line to create a border effect, so that yellow parts of the route are spottable on yellow streets. But, even if the black line is as thick as the route line, the whole route looks like a worm (very ugly). I tought this was because I was drawing lines from waypoint to waypoint, instead using the last waypoint as the next starting waypoint. That way if there is a couple of waypoints missing, the route will still have no cuts. What do I need to do to display both lines without a worm effect? -(void) drawRect:(CGRect) rect { CSRouteAnnotation* routeAnnotation = (CSRouteAnnotation*)self.routeView.annotation; // only draw our lines if we're not int he moddie of a transition and we // acutally have some points to draw. if(!self.hidden && nil != routeAnnotation.points && routeAnnotation.points.count > 0) { CGContextRef context = UIGraphicsGetCurrentContext(); Waypoint* fromWaypoint = [[Waypoint alloc] initWithDictionary:[routeAnnotation.points objectAtIndex:0]]; Waypoint* toWaypoint; for(int idx = 1; idx < routeAnnotation.points.count; idx++) { toWaypoint = [[Waypoint alloc] initWithDictionary:[routeAnnotation.points objectAtIndex:idx]]; CLLocation* fromLocation = [fromWaypoint getLocation]; CGPoint fromPoint = [self.routeView.mapView convertCoordinate:fromLocation.coordinate toPointToView:self]; CLLocation* toLocation = [toWaypoint getLocation]; CGPoint toPoint = [self.routeView.mapView convertCoordinate:toLocation.coordinate toPointToView:self]; routeAnnotation.lineColor = [fromWaypoint.weather getTemperatureColor]; CGContextBeginPath(context); CGContextSetLineWidth(context, 3.0); CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor); CGContextMoveToPoint(context, fromPoint.x, fromPoint.y); CGContextAddLineToPoint(context, toPoint.x, toPoint.y); CGContextStrokePath(context); CGContextClosePath(context); CGContextBeginPath(context); CGContextSetLineWidth(context, 3.0); CGContextSetStrokeColorWithColor(context, routeAnnotation.lineColor.CGColor); CGContextMoveToPoint(context, fromPoint.x, fromPoint.y); CGContextAddLineToPoint(context, toPoint.x, toPoint.y); CGContextStrokePath(context); CGContextClosePath(context); fromWaypoint = toWaypoint; } [fromWaypoint release]; [toWaypoint release]; } } Also, I get a <Error>: CGContextClosePath: no current point. error, which I think is bullshit. Please hint me! :)

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  • How to improve performance

    - by Ram
    Hi, In one of mine applications I am dealing with graphics objects. I am using open source GPC library to clip/merge two shapes. To improve accuracy I am sampling (adding multiple points between two edges) existing shapes. But before displaying back the merged shape I need to remove all the points between two edges. But I am not able to find an efficient algorithm that will remove all points between two edges which has same slope with minimum CPU utilization. Currently all points are of type PointF Any pointer on this will be a great help.

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  • is an instance variable in an action of a controller available for all the controllers view?

    - by fenec
    I am just trying to printout the parameters that have been entered into my form. basically i create a new bet then i display the parameters: MIGRATION enter code here class CreateBets < ActiveRecord::Migration def self.up create_table :bets do |t| t.integer :accepted ,:default = 0 t.integer :user_1_id #proposer t.integer :user_2_id #receiver t.integer :team_1_id #proposer's team t.integer :team_2_id #receiver's team t.integer :game_id t.integer :winner t.integer :amount t.timestamps end end def self.down drop_table :bets end end CONTROLLER bets_controller.erb enter code here class BetsController < ApplicationController def index redirect_to new_bet_path end def new @b=Bet.new end def create @@points=params[:points] @@winner=params[:winner] end end VIEWS New.erb New Bet <% facebook_form_for Bet.new do |f| %> <%= f.text_field :amount, :label=>"points" %> <%= f.text_field :winner, :label=>"WinningTeam" %> <%= f.buttons "Bet" %> <% end %> create.erb enter code here points:<%= @@points %> <br> winner:<%= @@winner %>

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  • global static boolean pointer causes segmentation fault using pthread

    - by asksw0rder
    New to pthread programming, and stuck on this error when working on a C++&C mixed code. What I have done is to call the c code in the thread created by the c++ code. There is a static boolean pointer used in the thread and should got free when the thread finishes. However I noticed that every time when the program processed into the c function, the value of the boolean pointer would be changed and the segmentation fault then happened due to the free(). Detail code is as follows: static bool *is_center; // omit other codes in between ... void streamCluster( PStream* stream) { // some code here ... while(1){ // some code here ... is_center = (bool*)calloc(points.num,sizeof(bool)); // start the parallel thread here. // the c code is invoked in this function. localSearch(&points,kmin, kmax,&kfinal); // parallel free(is_center); } And the function using parallel is as follows (my c code is invoked in each thread): void localSearch( Points* points, long kmin, long kmax, long* kfinal ) { pthread_barrier_t barrier; pthread_t* threads = new pthread_t[nproc]; pkmedian_arg_t* arg = new pkmedian_arg_t[nproc]; pthread_barrier_init(&barrier,NULL,nproc); for( int i = 0; i < nproc; i++ ) { arg[i].points = points; arg[i].kmin = kmin; arg[i].kmax = kmax; arg[i].pid = i; arg[i].kfinal = kfinal; arg[i].barrier = &barrier; pthread_create(threads+i,NULL,localSearchSub,(void*)&arg[i]); } for ( int i = 0; i < nproc; i++) { pthread_join(threads[i],NULL); } delete[] threads; delete[] arg; pthread_barrier_destroy(&barrier); } Finally the function calling my c code: void* localSearchSub(void* arg_) { // omit some initialize code... // my code begin_papi_thread(&eventSet); // Processing k-means, omit codes. // is_center value will be updated correctly // my code end_papi_thread(&eventSet); // when jumping into this, error happens return NULL; } And from gdb, what I have got for the is_center is: Breakpoint 2, localSearchSub (arg_=0x600000000000bc40) at streamcluster.cpp:1711 1711 end_papi_thread(&eventSet); (gdb) s Hardware watchpoint 1: is_center Old value = (bool *) 0x600000000000bba0 New value = (bool *) 0xa93f3 0x400000000000d8d1 in localSearchSub (arg_=0x600000000000bc40) at streamcluster.cpp:1711 1711 end_papi_thread(&eventSet); Any suggestions? Thanks in advance!

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  • SQL Query Math Gymnastics

    - by keruilin
    I have two tables of concern here: users and race_weeks. User has many race_weeks, and race_week belongs to User. Therefore, user_id is a fk in the race_weeks table. I need to perform some challenging math on fields in the race_weeks table in order to return users with the most all-time points. Here are the fields that we need to manipulate in the race_weeks table. races_won (int) races_lost (int) races_tied (int) points_won (int, pos or neg) recordable_type(varchar, Robots can race, but we're only concerned about type 'User') Just so that you fully understand the business logic at work here, over the course of a week a user can participate in many races. The race_week record represents the summary results of the user's races for that week. A user is considered active for the week if races_won, races_lost, or races_tied is greater than 0. Otherwise the user is inactive. So here's what we need to do in our query in order to return users with the most points won (actually net_points_won): Calculate each user's net_points_won (not a field in the DB). To calculate net_points, you take (1000 * count_of_active_weeks) - sum(points__won). (Why 1000? Just imagine that every week the user is spotted a 1000 points to compete and enter races. We want to factor-out what we spot the user because the user could enter only one race for the week for 100 points, and be sitting on 900, which we would skew who actually EARNED the most points.) This one is a little convoluted, so let me know if I can clarify further.

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  • R data.frame with stacked specified titles for latex output with xtable

    - by hhh
    > w<-data.frame(c(0,0,1,1.3,2.1), c(0,0.6,0.9,1.6091,1.6299), c(258,141,206.4,125.8,140.5), c(162,162.7,162.4,162,162)) > colnames(w) <- c('Worst Cum', 'Best Cum', 'Worst Points', 'Best Points' ) Wrong (the code) Worst Cum Best Cum Worst Points Best Points 1 0.0 0.0000 258.0 162.0 2 0.0 0.6000 141.0 162.7 3 1.0 0.9000 206.4 162.4 4 1.3 1.6091 125.8 162.0 5 2.1 1.6299 140.5 162.0 Goal: how? CUM Points Worst Best Worst Best 1 0.0 0.0000 258.0 162.0 2 0.0 0.6000 141.0 162.7 3 1.0 0.9000 206.4 162.4 4 1.3 1.6091 125.8 162.0 5 2.1 1.6299 140.5 162.0 Trial 1: fail with many data.frames > a<-data.frame(c(0,0,1,1.3,2.1), c(0,0.6,0.9,1.6091,1.6299)) > b<-data.frame(c(258,141,206.4,125.8,140.5), c(162,162.7,162.4,162,162)) > c<-data.frame(cbind(a,b)) > colnames(c) <- c('Cum', 'Points') > colnames(a) <- c('Worst', 'Best') > colnames(b) <- c('Worst', 'Best') and > xtable(c) % latex table generated in R 2.13.1 by xtable 1.6-0 package % Thu Nov 24 03:43:34 2011 \begin{table}[ht] \begin{center} \begin{tabular}{rrrrr} \hline & Cum & Points & NA & NA \\ \hline 1 & 0.00 & 0.00 & 258.00 & 162.00 \\ 2 & 0.00 & 0.60 & 141.00 & 162.70 \\ 3 & 1.00 & 0.90 & 206.40 & 162.40 \\ 4 & 1.30 & 1.61 & 125.80 & 162.00 \\ 5 & 2.10 & 1.63 & 140.50 & 162.00 \\ \hline \end{tabular} \end{center} \end{table} > xtable(a) % latex table generated in R 2.13.1 by xtable 1.6-0 package % Thu Nov 24 03:45:06 2011 \begin{table}[ht] \begin{center} \begin{tabular}{rrr} \hline & Worst & Best \\ \hline 1 & 0.00 & 0.00 \\ 2 & 0.00 & 0.60 \\ 3 & 1.00 & 0.90 \\ 4 & 1.30 & 1.61 \\ 5 & 2.10 & 1.63 \\ \hline \end{tabular} \end{center} \end{table} It is wrong because it replaces the inner headers with higher-level header nb "NA" vals.

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  • Estimating the boundary of arbitrarily distributed data

    - by Dave
    I have two dimensional discrete spatial data. I would like to make an approximation of the spatial boundaries of this data so that I can produce a plot with another dataset on top of it. Ideally, this would be an ordered set of (x,y) points that matplotlib can plot with the plt.Polygon() patch. My initial attempt is very inelegant: I place a fine grid over the data, and where data is found in a cell, a square matplotlib patch is created of that cell. The resolution of the boundary thus depends on the sampling frequency of the grid. Here is an example, where the grey region are the cells containing data, black where no data exists. OK, problem solved - why am I still here? Well.... I'd like a more "elegant" solution, or at least one that is faster (ie. I don't want to get on with "real" work, I'd like to have some fun with this!). The best way I can think of is a ray-tracing approach - eg: from xmin to xmax, at y=ymin, check if data boundary crossed in intervals dx y=ymin+dy, do 1 do 1-2, but now sample in y An alternative is defining a centre, and sampling in r-theta space - ie radial spokes in dtheta increments. Both would produce a set of (x,y) points, but then how do I order/link neighbouring points them to create the boundary? A nearest neighbour approach is not appropriate as, for example (to borrow from Geography), an isthmus (think of Panama connecting N&S America) could then close off and isolate regions. This also might not deal very well with the holes seen in the data, which I would like to represent as a different plt.Polygon. The solution perhaps comes from solving an area maximisation problem. For a set of points defining the data limits, what is the maximum contiguous area contained within those points To form the enclosed area, what are the neighbouring points for the nth point? How will the holes be treated in this scheme - is this erring into topology now? Apologies, much of this is me thinking out loud. I'd be grateful for some hints, suggestions or solutions. I suspect this is an oft-studied problem with many solution techniques, but I'm looking for something simple to code and quick to run... I guess everyone is, really! Cheers, David

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