# Tagged Questions

Questions on using or implementing more or less common data structures such as linked lists, structs, trees, tries, heaps etc. in Mathematica.

74 views

### DownValues Type Access and Timing

I definitely use so much DownValues structure for some many applications like to replace some common structures in a some way. It seems that DownValues is so fast for access, and set. My question is ...
118 views

### Extracting “records” from a matrix

From a rank 3 matrix like ...
998 views

### What is the Mathematica way of joining two tables?

Is there a special Mathematica way of joining tables of data together, so that I would get similar functionality as if I was running a database with sql? For example, I have one particular table here,...
1k views

### Get positions of all non zero matrix elements

I want to find all non zero elements of a table and I want to create a list that contains the name of the table the element was removed from, the position of the element, and the value of the element. ...
108 views

### Matrix Operation

I have a $3\times3$ matrix A, and a function sTrans that outputs two $3\times3$ matrices in a list when given a $3\times3$ ...
1k views

### Interpolation: Unstructured grid error

If I try to make a table SimpleTable and to interpolate a function of two variables, I encounter a problem. For example: ...
379 views

### Re-arranging / selecting of a data table very slow in For loop [duplicate]

My task is quite simple; I have a table of data like M = {{1,2}, {1,3}, {3,4}, {5,1}, {6,9}, {6,8}, {6,1}}; so the table is sorted with respect to the first ...
186 views

### Reading many single files and creating numbered (? or indexed) variable

I tried many different approaches, but I could not solve the following problems, I appreciate your help: What is the best way to read many data files? I mean we have ...
75 views

### Autoupdate Section Numbers? - Technical Document Authoring with Mathematica

Technical document authoring systems are structured ways to create, manage, and update documentation for various mediums such as print, pdf, web, etc. Take a look at this technical document ported to ...
175 views

### Return struct from function (with DownValues)

In Mathematica there is a way to create struct-like data type: struct[myField]=value I want to return myStruct from a function: ...
134 views

### Distances of locations in the matrix form

I want to have the distances of the cities in the matrix form.How can I have it for example for the cities like followings that also includes the distance of the city from itself which is zero: ...
797 views

### Efficient priority queues?

I'm trying to figure out how to transfer the concept of a priority queue to the functional world. Searches have turned up some implementations that use Append and other expense list copying techniques....
5k views

### Implementing a dictionary data structure

As one learns from a course on data structures, hash maps or dictionaries can be efficient when applied to appropriate tasks. I need a hash map in Mathematica and I've never found it. I'm scratching ...
75 views

### Efficiently generating 3D histograms for large sets 2D coordinates [duplicate]

I'm attempting to generate a 3D histogram for a large set of two-dimensional coordinates ($\approx 10^7$). the x- and y-components of each coordinate are rounded to the nearest integer, and these ...
1k views

### Import Spreadsheet Data and DeleteCases of empty cells &/or choosing a Range to import

I am importing Excel spreadsheet data into Mathematica. Here is what the data looks like, notice the cell Q1 with "sdf": I import this data by specifying the Spreadsheet location, sheet name, top ...
125 views

### Mean of Date variable data

I have hourly registered data as : ...
201 views

### Error in ARIMAProcess example

I am trying to compile the sample of ARIMAProcess of MMA here .It doesn't work.What is wrong?Could you please help?I am using exact same code. ...
118 views

### DateListPlot input entry problem

I imported some data from Excel and got the following for my date and values: {{{1986, 1, 2, 0, 0, 0.}, 25.56, ""}, {{1986, 1, 3, 0, 0, 0.}, 26., ""} It seems ...
413 views

### How to determine cluster membership using FindClusters?

I have a 1000 by 3 data matrix in which for each person we have 3 scores. I want to cluster those persons into 8 cluster using Agglomerative method. I did the clusetring by: ...
262 views

### Is there a method to enumerate the keys/values of SystemUtilitiesHashTable

Lacking from the simple API of SystemUtilitiesHashTable is a method to enumerate the keys/values. ...
195 views

### What is the fastest way to maintain a large set of expressions?

In my algorithm I need to maintain a set (an unordered list of distinct elements) of expressions supporting two operations: Test an expression for membership in the set Adding a new expression to ...
158 views

### How to convert a spaceless data into tab delimited

I have a data set in form of:(this is just an example) 1324501020 3241030205 4332020134 the data are stored in a text file (e.g. data.txt) but I need to convert ...
282 views

### Distribute and analyze large datasets

I need to analyze very large datasets, and they obviously don't fit in a computer memory. I need to produce some statistics on these datasets, and this brings me here: How can I make some statistical ...
289 views

### Efficient way to solve equal sums $x_1^k+x_2^k+\dots+x_5^k=y_1^k+y_2^k+\dots+y_5^k$ with Mathematica?

I need to solve the system of equations, call it $S_1$, in the integers $$x_1x_2x_3x_4x_5 = y_1y_2y_3y_4y_5$$ $$x_1^k+x_2^k+\dots+x_5^k=y_1^k+y_2^k+\dots+y_5^k,\;\; k= 2,4,6$$ I used a very ...
469 views

### How to populate a table using a rule replacement

I am trying to populate the rows and columns of a table by using a rule replacment. To generate a table that looks like this For example Sc would be row 1, column 1. An example of a record looks ...
387 views

### DownValue “associative array” to list? [duplicate]

I have a "sparse array" like this arr[1.5]=0.4, arr[3.5]=0.7, arr[7]=0.3 which is not really a sparse array since the keys are not all integers. This is like a ...
275 views

### Efficient Data Entry / Manipulation with Many Datasets

I currently have a simple task of graphing many different datasets (26 here, with many different instances where I'll need to do, say, 26 different ones from the same template). I'm trying to ...
310 views

### How do I create a graph with randomly directed edges starting from a undirected graph?

I have an undirected graph $G$. How would I randomly assign directions to some fraction $p$ of the edges? How might I do this efficiently / quickly provided I have a large graph structure? For ...
191 views

### Iterating Reads From a Text File and Writing the Results of Operation

I have a very large text (TSV) file. I am able to now read single line, thanks to StackExchange. I am able to read a part of that line using the part operator. I want to iterate through the whole file,...
315 views

### Data structure for a list of actions [closed]

The idea: I need to generate a sequence of events then run a "propagator" over the list of events where the "propagator" will update the state of the following event. I can then write functions that ...
437 views

### Read a file into a list of vectors [closed]

I have file structured as (Axis 1) (Axis 2) Data. As an example: ...
649 views

### Efficient code for tallying entries in very large lists

I am dealing with data sets containing tens of millions of (hashable) entries and simply using the Tally function to count the frequency of each unique list element ...
319 views

### Processing and storing a graph with a large number of vertices s.t. k-hop neighborhoods are efficiently retrievable

I have an unweighted, undirected graph $G$ with $(v_1, ..., v_N) \in V$ vertices, where each vertex in the lattice represents a string of some length ($\leq 200$ characters), and I need to construct \$...
674 views

### Creating a R DataFrame like construct in Mathematica

I kept getting my data mixed up so I decided to see if I could construct a package adding a R DataFrame like construct to Mathematica. I managed to cobble something together that sort of works, but I'...
941 views

### pointer like operations in mathematica and evaluation control

I would like to create a data structure of the type "header[pointer]" where pointer would point to a list. I will shown on an example how I'd like this to work, and where the problems are. ...
354 views

### Initialization Time Out (Weighted Financial Data)

I've been playing with WeightedData and wanted a financial engineering example, a colleague suggested working with the fractional return (...
1k views

### Efficient circular buffer?

I wish to create an efficient circular buffer. That is, I wish to keep a fixed length list while appending a new value and dropping the oldest, repeatedly. As we know lists in Mathematica are ...
261 views

### How can I create Arguments Maps with Mathematica's graph functions?

I am relatively new to Mathematica, and I would like to know how I could use it to represent an Argument Map, such as those that you generate on online tools such as http://debategraph.org. The ...
271 views

### Accessing the Data of an RLink RDataFrame

I am trying to extract the data table itself from an RLink-generated RDataFrame: ...
291 views

### Return a Part by Reference? (For accessing hierarchical / structured data)

Is there a way to return a part of a list by reference, for reading and writing? I want to do this so I can easily manipulate "rule-styled structured", i.e., hierarchical data that is loaded from a ...
718 views

### How can a big table be treated as a database?

I often work with big tables that I want to treat kind of like a database. Here's an example table. ...
1k views

### Emulating R data frame getters with UpValues

What's the best way to emulate R's data frames functionality? This includes the ability to select rows and columns in a 2-dimensional table by the string identifiers positioned typically in the first ...
578 views

### How to get the list of defined values for an indexed variable?

I would like a table with rational indexes - thus it would be practical to use a dictionary, which, in Mathematica are implemented with the indexed variables. I would like to be able to do: ...
284 views

### Access pairs of vectors, rather than the matrices, in partitioned data structure at a levelspec

I have some old code to analyze correlation between 2 time series by looking at windows of different lengths shifting across the time series data. The code: gets 2 sets of time series data (in ...
4k views

I have a large Excel .xls file. Miniature version shown below: (formatting should appear as two columns...) ...
662 views

### Mouse motion heat map - live visualization and analysis

Mouse motion heat map is an great way to study spatial attention distribution, styles of movement, reaction, etc. I am trying to design a code that visualizes such heat map. The requirements: 1) It ...
587 views

### How to get complete Documentation Center graph of guide pages?

On the very last image below you can see a typical path of walking through Documentation Center guide pages. What is the best way to get the graph data and visualize the whole structure of these ...
855 views

### Question about designing a particular data structure

Background: I store polygons with a color assigned at the face level. In some occasions I want to use vertex colors but I want to store data efficiently, i.e. don't want to duplicate data to the ...