# Tagged Questions

Questions on the manipulation of List objects in Mathematica, and the functions used for these manipulations.

741 views

### Counting sublists containing 0

Given a list: data = {{0, 2}, {0, 0}, {1, 0}, {1, 2}, {2, 3}}. I would like to count the number of sublists which contain zero. ...
516 views

### Dropping n consecutive terms from a list periodically

Suppose I have the following list lis = Range[100]; and I want to remove n consecutive terms periodically from the list. For example suppose I want to drop terms ...
1k views

### How to thread a list

I have data in format data = {{a1, a2}, {b1, b2}, {c1, c2}, {d1, d2}} Tableform: I want to thread it to : ...
415 views

### I have the minimum Y value. I want to find the corresponding X value from the list [duplicate]

I have a very big file and contains data in the format of {x,y}. I got the minimum Y value by using data[[All, 2]] // Min[#] & Now I want to get the X value ...
3k views

### Most Efficient Way to Calculate the Product of All Items in a List?

Say that I have a list of returns on a financial asset over time and want to know the total compounded return. To get the answer, I need to add 1 to each return and then calculate the product of all ...
1k views

### Building a continued fraction

I've completed a problem that involves approximating $e$ by a continued fraction: $$\frac{N_1}{D_1+\frac{N_2}{D_2+\frac{N_3}{\ddots+\frac{N_k}{D_k}}}}$$ with the $N_i$ being the list ...
848 views

### How to sort digits in a string while keeping other characters untouched?

Now there is a string with digits and letters, for instance, "95uge678r3gi89hgfe30kgh063d51". And the expected output is ...
488 views

### Product of elements of a list

Sum is for functions; Total is for a list. Product is for a function; what is the command ...
370 views

### How to evaluate the second argument of Cases only once

I'd like to find a fast but readable way to achieve the following: ...
1k views

### Splitting up delimited data in lists

One task that I frequently find myself doing in Mathematica is splitting lists into lists of sublists, using specific elements to define the break-points. This is particularly useful with imported ...
428 views

### Concatenation of lists in a Fibonacci-like pattern

I am trying to create a List of elements that follow the general pattern: $$X_{n+1} = X_n X_{n-1}$$ where the operation on the right hand side is concatenation, i.e., joining. I want to achieve the ...
912 views

### Subtracting two plots from each other after shifting one

I have the following lists representing energy spectra that need to be subtracted from each other to produce a difference spectrum. ...
724 views

### Sort+Union on a list

Probably this is too trivial question for this forum but for some reason I am not getting it on my Mathematica 7 so far. I have a list ...
927 views

### Specifying string patterns in DeleteCases

It seems that DeleteCases is not compatible with string patterns, at least directly (see, for example, this question). Is this true? If so, why is this the case? ...
373 views

A friend of mine showed me this example, it's a test comparing LengthWhile to a self-made lengthwhile written in a direct and ...
2k views

### Reshape vectors exactly like in MATLAB

This gives a 64×1 column vector in Mathematica: ...
3k views

### Selecting every n-th element from a list

I have a list: data = {4, 5, 7, 8, 9, 5, 3, 2, 1, 2, 13, 12}; I want to take those elements in the list which are located at equal distances, say, every third ...
480 views

### How can I collect data for visualization of quick sort?

I know how to implement quick sort in Mathematica. But I don't know how to get the temp data for visualization, because I used recursion. I want the effect similar to this: ...
2k views

### How do I find the elements in a list that return the highest value for a function?

Suppose we have a list of values and a function f. I want to find which of the elements maximizes the return value of the function in Mathematica. Let call the ...
445 views

### How to fill a grid make its total be largest

I have a blank grid whose dimension is 5*5. I want to fill it with some number using 1, 2, 3 and 4. But in every blank space if you fill 2, its neighbor (include four direction, such as left, right,...
390 views

### The gap between MapAt and ReplacePart for 2D data tables with headers

Consider a relational table derived from survey data, where each column ("001-01" ...) represents a responder and each row (...
1k views

### What is the most efficient way to map a linked list?

In order to work with lists effectively using common recursive patterns from functional programming, it's often most convenient to worked with the "linked list" representation, that looks like this: <...
405 views

### Simple way to concatenate Dataset columns

Consider these two datasets: d1 = Transpose@Dataset[<|"a" -> Range[5]|>]; d2 = Transpose@Dataset[<|"b" -> Range[5, 1, -1]|>]; {d1, d2} What's ...
230 views

### Unexpected slowness checking for empty list?

I thought I had a firm understanding of the differences between Equal and SameQ, but this has me puzzled: ...
566 views

### What is the fastest way to get the nth distinct permutation of a list?

What is the fastest way to write a function nthPermutation[xs_List, n_Integer] which is equivalent to Permutations[xs][[n]] but ...
844 views

### Vlookup function as Excel in Mathematica

How can we create a Vlookup function, similar to what we have in Excel? So if we have a table a and another b, we could add ...
766 views

### How to split a Dataset into training and testing for machine learning?

Suppose I have iris data In the Dataset Format. How to split the iris data Into training and testing for Machine learning? For example,Transform the data for Classify.
244 views

### Unexpected behavior of Sequence — using Sequence to delete parts of an expression

I thought that assigning Sequence[] to the part of an expression was an effective way to remove it. For example, the following code yields {2,3,4,5}: ...
650 views

### Brackets around each item in matrix

I have a matrix where every item in the matrix has its own brackets that I do not want. How can I remove the brackets around each item?
646 views

### How to group each element with each consecutive elements in one head

Suppose I have the following list: list = {a, b, c, d} I want to generate this result: ...
884 views

### Is there a way to riffle more than two lists?

I thought Riffle would generalize such that Riffle[{a,b,c},{1,2,3},{x,y,z}] would return ...
599 views

### How to pick increasing numbers from the list

How to pick increasing numbers from the list. lst = {5, 3, 6, 2, 7, 4, 8}; out: {5,6,7,8} So many interesting ...
346 views

I have a ragged list ragged = {{a,b,c,d,e},{x,y,z}} that I would like to trim (on the right) to be rectangular. The desired result is ...
697 views

### Filtering elements from a list that appear only once

I want to be able to select elements from a list that only appear once. I originally had this: Select[Table[Count[list, i], {i, list}], # == 1] But the issue is ...
3k views

### Combination and Permutation

How could I obtain the list of all the groups of 5 numbers taken from Range[12] such that the 2 lists have an empty intersection : ...
1k views

### How can I Flatten this List with Inner List of Lists?

Given the following List ...
2k views

### How can I simulate this animation of checking for prime numbers?

I can only implement a very simple one, I want to make my code look like that. Any better ideas? ...
1k views

### How to partition a list of numbers in two lists of numbers such that each lists elements sums up to the same number?

I have the following list of squares. {1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256} Their sum is $1496$, I want to make two partitions ...
5k views

### How to create a list of pairs from 1d list(s)?

Say I've got two 1-dimensional lists A = {1,2,3} B = {a,b,c} How do I create a list of all pairs from list A such that the ...
838 views

### Deleting Lonely Numbers From a List

Suppose I have a list of integers like so: list = {1,2,5,6,8,10,11,12,14,16,17,18,19}; I'd like a function that will take this list and return a new list with ...
265 views

### Using 0 to create new columns in a list with Part

I just discovered a nice way to create intermediary columns in a list, and I would like to know if I can have some problem with it. It Works like this: Imagine I have this list, 5x3: ...
950 views

### Using Position (which requires a pattern) in the same manner as Select (which requires a criterion)

I am using Mathematica7. I have a list of lists (creatively named list in the following sample code) containing data. I would like to find the positions of the ...
475 views

### How would you efficiently implement BinListsBy?

Let's say I have a list like this: data = {{21, "Alice"}, {27, "Bob"}, {22, "Charles"}, {34, "Dora"}, {75, "Eliza"}} containing ages and names of persons. What I ...
526 views

### how to permute list of number{1,2,3,…,n},while preserve the order of first m terms as well as the last n-m terms?

For example, starting from {1,2,3,4}, I want to generate all permutations like {1,3,2,4},{1,3,4,2},{3,4,1,2} which preserve the ...
863 views

### How to add lists with unequal length?

Given lists of unequal lengths, I want to add them together element-wise, treating missing elements as zero. For example, {1, 2, 3} + {a, b} + {x} should give ...
648 views

### What's the function that takes X[Y[z___]] to Y[X[z___]]? (“swap heads”)

I've seen the operation described in the title before (basically, swap the heads of the first two levels of an expression), but I can't find it... Does anyone know the function (or idiom/incantation) ...
231 views

### Exclude overlapping lists while keeping disjoint- and sub-lists?

Consider a function f[l1_List,l2_List] which is given lists of integers. Whenever two of the lists contain completely disjoint sets of integers OR one of the lists ...
5k views

### Removing empty sets from lists

If I had a list, say, names= {"Andy", "Bob", "Carly", "Sandy", "Jeff", "Tim", "Tom", "Zach"} and I decide to pick a characteristic only a certain of them have, ...