in which column is an entry?

Hi,

df  is a data.frame with 43 colums and 29877 rows with lot of NA.
I want the column number for all respondendts in one column 
where is the first entry >=0 as columnnumber.

my first step:
 time <- function(df)
+     {        for (i in 1:length(df [,1])) {    
+     which(df[i,1]:df[i,43] >= 0)
+     }
+            }

t1 <-  time(YS)

Error in df[i, 1]:df[i, 43] : NA/NaN argument

Many thanks for help , regards christian