e.g. .csv file like this
col1,colX,NA,NC,AN,nA
23,asd,df,sdf,asdf,sadf
23,asd,df,sdf,asdf,sadf
23,asd,df,sdf,asdf,sadf
23,asd,df,sdf,asdf,sadf
>tt <- fread("NA_test.csv")
>t
col1 colX V3 NC AN nA
1: 23 asd df sdf asdf sadf
2: 23 asd df sdf asdf sadf
3: 23 asd df sdf asdf sadf
4: 23 asd df sdf asdf sadf