Statistics and Data Analysis for Microarrays Using R and Bioconductor, 2nd Edition

Introduction to R 129

Also, the raw number of citations is clearly dependent on the numb er of papers

published. It is clear that if a journal publis he s more papers, the likelihood

of subsequent c itations is higher. Hence, we nee d to normalize the number of

citations to the number of papers published in each journal. In R, this can be

achieve very easily as follows:

> impact.factors = cites/articles

> impact.factors

[1] 4.33870967742 3.93884892086 6.01894317049

In the above expression, the dot character, “.”, is used a part of the array

name and does not have any other special meaning. Note that even though

the syntax used the names of the arrays containing the data, the result is an

array of values obtained by dividing each element of the first