Questions tagged [list-manipulation]
Questions on the manipulation of List objects in Mathematica, and the functions used for these manipulations.
6,776
questions
19
votes
8answers
919 views
How can I remove B -> A from a list if A -> B is in the list?
I have a list of transformations like this:
list = {"A" -> "B", "B" -> "A", "C" -> "D"}
As this is used to plot an undirected graph with ...
8
votes
4answers
330 views
Check in a series if there exists adjacent values with less than a certain number of missing values
I'm working with a large number of series of different experiments, where there exist a lot of experiments where there are no entries. I now want to draw a sample where there should exist at least ...
41
votes
7answers
12k views
How to Delete Elements from List1 appearing in List2?
I'm new to functional programming of Mathematica and trying to remove one list of assorted elements from another. However I only find functions working with the Index rather than the values itself:
...
24
votes
7answers
2k views
Permutations[Range[12]] produces an error instead of a list
This input:
Permutations[Range[12]]
Results in this (error) output:
...
23
votes
8answers
2k views
Selectively Mapping over elements in a List
I am using the following code to easily generate a row of images of all eight planets of our Solar System:
...
6
votes
1answer
200 views
Bug in LengthWhile?
Bug introduced in 8.0.0 and fixed in 8.0.1
Is this a bug or my MMA went insane or I'm missing something?
LengthWhile[Reverse@IntegerDigits[1000], # == 0 &]
...
27
votes
7answers
3k views
Efficient way to count the number of zeros at the (right) end of a very large number
If I want to count the number of zeros at the (right) end of a large number, like $12345!$, I can use something like:
Length[Last[Split[IntegerDigits[12345!]]]]
...
20
votes
6answers
2k views
On generalizing Partition[] (with offsets) to sublists of unequal length
The usual Partition[] function is a very handy little thing:
...
2
votes
4answers
12k views
Creating a data1 versus data2 plot?
I have a table of data with multiple rows and columns, and I have to make a versus data table using two of these columns. Essentially, I have to set one column of data (column 3) as the y-axis and ...
12
votes
7answers
4k 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 :
...
22
votes
2answers
3k views
Finding a subsequence in a list
I have a list and I want to find (in this particular case the first) appearance of a any of some subsequences, of possible different lengths. None of the subsequences is a subsequence of each other.
...
17
votes
7answers
5k views
How to find rows that have maximum value?
Suppose if I have following list
{
{10,b,30},
{100,a,40},
{1000,b,10},
{1000,b,70},
{100,b,20},
{10,b,70}
}
How to find rows that have max value in ...
14
votes
3answers
4k views
Flatten at a certain level
In an earlier question the brainteasing fourth syntax variant of Flatten was discussed. I see that with
...
14
votes
3answers
4k views
Why don't * and ^ work as I expected on matrices? [closed]
For example, this input...
{{1, 2}, {3, 4}}*{{1, 2}, {3, 4}}
produces this output...
{{1, 4}, {9, 16}}
and this input...
<...
9
votes
4answers
401 views
Unexpected behavior from GatherBy in version 7
Bug introduced in 7.0 or earlier and fixed in 8.0.4 or earlier
I have come across what appears to be a bug in GatherBy. It appears similar to the problem of using ...
10
votes
2answers
513 views
How to generate Intervals from a given list?
If I have a list
list={3,7,4,5,1}
how to get the List of Intervals /Ranges
result = {{1,3},{3,4},{4,5},{5,7}}
12
votes
13answers
2k views
How to find range in which a number falls, from given list of numbers?
How can one find the range in which a number falls, from given list of numbers?
...
18
votes
7answers
877 views
Elegantly pairing up mismatched lists
HistogramList returns a list of bin boundaries and a list of counts. There is one more boundary than counts, and I'd like to pair them up so I can feed it into <...
20
votes
3answers
2k views
Efficient way to combine SparseArray objects?
I have several SparseArray objects, say sa11, sa12, sa21, sa22, which I would like to combine into the equivalent of {{sa11, sa12}, {sa21, sa22}}.
As an example, I ...
41
votes
5answers
19k views
What is the most efficient way to add rows and columns to a matrix?
Say I have a matrix m and a vector v.
...
69
votes
9answers
55k views
How to find the position of elements in a list satisfying criteria
Say I have a list x={2,4,6,8,10} and I want to find out the positions of the elements that are greater than 7.
...
11
votes
5answers
2k views
How do you efficiently return all of a List but one element?
I have a problem that I am working on that requires that I compare several lists of overlapping data points. As I traverse one of the lists, I'd like to only compare those data to the other lists, and ...
101
votes
4answers
5k views
Flatten command: matrix as second argument
One thing I could never wrap my head around is how Flatten works when provided with a matrix as the second argument, and the Mathematica help isn't particularly ...
20
votes
7answers
2k views
How to use Union on list of lists without sorting them first?
If I do
ClearAll[a, d]
lsts = {{a, d}, {a, d}};
Union[lsts]
I get the expected answer
{{a, d}}
but if I do
...
20
votes
2answers
1k views
Data Table Manipulation in Mathematica: Step 2
In this previous post (Data Table Manipulation in Mathematica) we find the brilliant suggestion proposed by Leonid Shifrin that allows to select specific rows identified by the header name.
I'm now ...
42
votes
3answers
6k views
Data Table Manipulation in Mathematica
I am a statistician searching for an efficient way to select rows or columns from a table of data in Mathematica. Let me pose the question in 2 parts with a SQL-style table of data:
...
