Column names in vector are missing

username

I have a dataframe with this format:

DF1 <- DF0[i,6:12]  (DF0 is the original data frame I read from)

The resulting DF1 has the following names:

DF1:  
home - train -bus -car  .. - male - female
1       3      0              0       1

What I want to do is restore the names of the columns that are 0, for example:

colNull <- colnames(DF1[,DF1==0])

My understanding is that this generates a series of "values" (since in most DF0 rows, several columns are 0):

colNull   like  'bus','male'.....   (char type)

However, when there is only one column in DF1 with 0, the column name is no longer restored, and the result colNull is NULL (class(colNull is also NULL)), which I cannot use.

Is there an easy fix? I would also like to understand why this is happening, or what I am doing wrong. I know this has to do with the object format, not the reasoning behind it.

Thanks in advance, p.

Akron

When we subset a dataset with a single row or if the output is a single column, reduce it to a vector when subsetting. Based on the default options ?"["are

  x[i, j, ... , drop = TRUE]

so eithernames

 names(DF1[,DF1==0])
 #[1] "bus"  "male"

or using drop=FALSEshould work

 colnames(DF1[,DF1==0, drop=FALSE])
 #[1] "bus"  "male"

Or another option is to use Convert Logical Matrix to Logical Vector and as.vectorit should work as expected.

 colnames(DF1[as.vector(DF1==0)])
 #[1] "bus"  "male"

Note: this is not the general case, since there are more than one line, we may need to usecolSums(DF1)==0

data

 DF1 <- data.frame(home=1, train=3, bus=0, male=0, female=1)

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