Averaged / grouped z-score for a column

Question

[454Casull]

Hi all,

I performed RNA-seq in 4 different cell populations. Then I plotted the normalized read count for a list of genes I'm interested in. The color code is the z-score of the 4 sample in each row (each gene). However, I'm wondering if there is a way I can get an averaged/grouped z-score for each column (each cell population), because in this way, I can tell whether the list of genes is more highly expressed in one sample compared to others. Does anyone know how to do it or can suggest some other method to do it? Any input is highly appreciated!

Best, Nina