怎样理解进行submap时的过滤方法：

For the log2 transformed ratio data generated by cDNA microarrays, we first removed genes whose values were missing in more than 5% of the samples, and then imputed the missing values for the rest of the genes using a k-nearest neighbor algorithm(ImputeMissingValues.KNN, in the GenePattern software package, GenePattern).

Before marker gene selection, we used following gene filtering. For the oligonucleotide array data, only genes exhibiting at least 3-fold differential expression and an absolute difference of at least 100 units across the samples in the experiment were included. For the cDNA array data, only genes with an absolute log2 ratio greater than one and whose difference in log2 ratio across all the samples in the data set was greater than one were included.
进行submap输入的表达矩阵基因怎样选择？