Thanks, Saul! That package 'data.table' works very well. It cannot read mat directly and I have to convert mat into csv firstly, but it reads csv very quickly. It did solve my problem!

Thanks again,

Lei

Mr. Lei,

May be you can try rmatio package available on guthub (link below).

Hope this will help to get rid of csv conversion.

https://github.com/stewid/rmatio

Thanks for your suggestion, Chintan. I have tested it, and unfortunately it took much longer time using 'read.mat' in 'rmatio' (I have waited for half an hour and it is still reading. By contrast, read csv using 'data.table' just took 10 minutes). But thanks anyway.