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

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

-----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
Envoy??: mercredi 24 d?cembre 2008 13:17
??: 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