Question

I have a table in R with the following structure:

ID var1 var2 var3 .... varN
AA  1    2    1          3
AB  0.2  1    4          1

…

How can I select only those rows where var1<2 and var2<2 and var3<2 and … varN<2 ?

Answer 1

If your dataframe is dat the test for all elements in a row being less than 2 and retruning only those rows would be:

dat[ apply( apply(dat[-1], 1, "<" ,2) , 2, all ), ]

The logic: the inner apply returns a logical matrix:

apply(dat[-1], 1, "<" ,2)
     [,1]  [,2]  [,3]
var1 TRUE  TRUE  TRUE
var2 TRUE FALSE  TRUE
var3 TRUE  TRUE FALSE
varN TRUE FALSE  TRUE

Notice that it is transposed in dimensions, since R matrices are constructed column-major order, so the outer apply needs to work on columns, hence the use of 2 as the INDEX for applying the all function. Testing:

 dat <- read.table(text="ID var1 var2 var3  varN
 BA  1  1  1  1
 AA  1    2    1          3
 AB  0.2  1    4          1", header=TRUE)

 dat[ apply( apply(dat[-1], 1, "<" ,2) , 2, all ), ]
#  ID var1 var2 var3 varN
#1 BA    1    1    1    1