[R] selecting a subset of a matrix based on a value occurring in 5 records

[Veslot Jacques]

> mat[,colSums(mat!=0)>=5]

Jacques VESLOT

CEMAGREF - UR Hydrobiologie

Route de Cézanne - CS 40061      
13182 AIX-EN-PROVENCE Cedex 5, France

Tél.   + 0033   04 42 66 99 76
fax    + 0033   04 42 66 99 34
email   jacques.veslot at cemagref.fr  


>-----Message d'origine-----
>De : r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] De la part
>de Bob Green
>Envoyé : mercredi 24 décembre 2008 13:17
>À : r-help at r-project.org
>Objet : [R] selecting a subset of a matrix based on a value occurring in 5 records
>
>
>Hello,
>
>>I am hoping for some advice as to how I might create a subset of a
>>matrix. The matrix is  176  x 3530. The rows are individual records
>>and the columns words. I want to create a new matrix that only
>>consists of words which occur in at least 5 records.  For example,
>>if column 7 is "charges" and this only appears in 4 records/rows
>>this variable would not be included, whereas if column 109 was the
>>word "monitor" and occurred in 95 records it would be saved into the
>>new matrix. Values in the matrix are  numbers, such that if a word
>>does not occur in a  record the cell contains a zero, whereas if it
>>occurs 7 times there is a value of 7 for that record. It is the
>>number of records rather than the than the column total that is the
>>criteria for determing inclusion into the matrix.
>
>
>Any suggestions on how I might reduce the size of this matrix so as
>to include only those columns in which a word occurs at least in 5
>records is much appreciated,
>
>regards
>
>Bob
>
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