Make a Table of Contents

Average and Standard Deviation for a Table or Spreadsheet

Module to find the average  and std deviation of a list of values. The list above (yvalues) is essentially a table or spreadsheet - here we will find the average and std deviation for each column of data:

There is an easier way to do this : Here we sum a column

Here we sum a row:

Create a Table with Column and Row Headings

Create a Graph with Text for the data points

This applies different sized labels to the plot

Emulate the VLOOKUP Function from Spreadsheets

How do you sum a specific column in a table, with filter critera? Here, we find all the unique values in the first column, and sum the desired column (basically a VLOOKUP in Excel.

a = {{a1, b1}, {a2, b2}, {a2, b3}, {a2, b4}, {a3, b5}, {a3, b6}};

You can use : els = Union@Part[Transpose@a, 1]
sel[x_] := Select[a, (#[[1]] == x) &];
Map[sel[#] &, els]
Map[{#[[1, 1]], Total@Transpose[#][[2]]} &, %]

Explanation : The first line finds the different first elements (e.g.{a1, a2, a3})

The function sel[x_] selects the rows of a which have x as their first
element.Then the first Map applies this function for the different first
elements : {a1, a2, a3}

Then the second Map constructs your final matrix with the different
elements in the first column and the sum in the second column.

Calculate Number of Days between Dates

Miscellaneous Functions

Import Tab - separated Data into a Formatted Grid

Sort an Array of Arrays by Column (position)

Graphs

Create a Histogram

Another way :

Sum a Specific Column, Conditionally

Playing with Text as DataPoints, Varying Size

Tooltips and Rollovers

Select a subset of rows from a list based upon a list of criteria chosen by the user.

I'm working on a small application and I'm searching for a way to  
Select a subset of rows from a list based upon a list of criteria  
chosen by the user.  Here is small (hypothetical) example. Say one  
has a data set of consisting of a list of as follows:

{ {1,A,Blue,"Hello",10.5},{7,D,Green,"Goodbye",9.4},
{6,S,Yellow,"Hello",6.9},{3,A,Blue,"Hello",8.0}}

The user will specify a letter and a color and the program should  
Select[ ] the appropriate rows, e.g., if I pick Color=Blue and Letter  
= A, then it will return

{ {1,A,Blue,"Hello",10.5},{3,A,Blue,"Hello",8.0}....}, etc.  Thus one  
can enter Select[myData,(#[[2]]==A && #[[3]]==Blue)&] and get the  
appropriate records.Note that The actual data set has about 20,000  
records (lists), each with about 20 fields, and can select 7 or 8  
different attributes, so the Select statements get fairly long.

My question involves an efficient way to code the Select statement if  
a user wants to chose records that correspond to any value of a  
particular field, e.g., All of the Color=Blue, regardless of the  
Letter choice,e.g.,

Select[myData,(#[[3]]==Blue)&]

More precisely, is there a way to pass Select the user choice of any  
letter using some sort of 'wildcard' value that represents any value  
for the specific attribute, i.e.,

  Select[myData,(#[[2]]=='Wildcard' && #[[3]]==Blue)&]

My motivation is that if I have may possible selection criteria, I  
can still use a single Select statement. Hi, try MatchQ[#[[3]], Blue] if you wist to select Blue
and MatchQ[#[[3]], _] as the wildcard.And
to make it more easy

try MatchQ[#[[3]],Blue] if you wist to select Blue
and MatchQ[#[[3]],_] as the wildcard. And
to make it more easy

mypattern={_,_,_,_,_};
...
If[characterSelectedQ,mypattern[[2]]=selectedCharacter];
If[colorSelectedQ,mypattern[[3]]=selectedColor];
...
Select[lst,MatchQ[#,mypattern] &]

This works

What to do with missing values in a list

Select Rows based on Criteria - Method 1

Select Rows based on Criteria - Method 2

End

Created by Wolfram Mathematica 6.0  (02 June 2008)