Linked Questions

7
votes
8answers
1k views

Merging lists and adding common elements [duplicate]

I have two 2D arrays where some of the x-values are identical, L={{1,1},{2,2},{3,3}}; J={{0,1},{2,2},{4,4}}; I want to add these lists in the following way <...
10
votes
5answers
3k views

Multidimensional interpolation with duplicate abscissa values [duplicate]

I am trying to do a first order interpolation on a multidimensional data set containing duplicate abscissa values (which Mathematica does not like), like this one: ...
5
votes
4answers
1k views

Combining the second elements of a set of ordered pairs based on their first element [duplicate]

I have a large set of ordered pairs and I am trying to add the second elements together for any group of pairs that has the same first element. For example my data looks like: ...
7
votes
3answers
371 views

Merging lists of pairs [duplicate]

I want to add several fluorescence spectra. They are lists of the format ...
5
votes
3answers
195 views

Add up data values for matching entries [duplicate]

Is there a function that extends Tally in the following way (essentially need an answer to this guy's homework question): the a <...
2
votes
3answers
442 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 ...
6
votes
2answers
149 views

Mathematical operation on two lists by a “key” [duplicate]

I'm a complete newb here. Just looking for direction. I've got two lists like this... ...
4
votes
1answer
1k views

List of tuples: group by first element of tuple; sum up the second element per group [duplicate]

Imagine following list list = {{0, 3}, {1, 1}, {1, 2}, {2, 3}, {2, 4}} I would like to get the result ...
3
votes
2answers
377 views

An conditional Sum of elements in Array [duplicate]

Consider we have: list = {{2, 3}, {3, 30}, {3, 2}, {4, 53}} and we want to compare the first elements and sum the second elements if first elements are similar ...
1
vote
2answers
437 views

Combining data sets by adding y values [duplicate]

Suppose I have the following list of data {{1,2},{1,5},{6,1},{1,3},{2,1},{2,2},{2,3},{5,4},{5,2}} This is similar to my actual data in that each x value has ...
1
vote
1answer
711 views

Frequency of elements in a list (merging tally data) [duplicate]

I've got a list in the format of list={{a,1},{a,1},{b,1},{c,1},{b,1}} And I want it to "compress" into a list of pairs ...
2
votes
2answers
181 views

Total elements of a list that have a common first element [duplicate]

Possible Duplicate: List-operations only when restrictions are fulfilled (Part 1) I have a set of data like: ...
1
vote
2answers
135 views

Gather elements in sublist by first element for the purpose of summing [duplicate]

I have data which looks like this: ...
1
vote
2answers
216 views

Given a list of date and value pairs, efficiently sum the values by date [duplicate]

I have a list of date & value pairs. There can be multiple entries for each day. Sample data can be generated with the following: ...
2
votes
1answer
75 views

Let's do this list-rearrangement prettier [duplicate]

Suppose that i have a list in this format= $list=\{ \{a,obj1 \} ,\{c,obj2 \}, \{a,obj3 \}, \{b,obj4 \} \dots\}$ I want to construct a new list in this way: $ newlist= \{ \{ \{a,obj1\} , \{a,obj3\} ....

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