R has gained popularity among data scientists and statisticans in last few years. Popular R packages are developed after rigorous testing and returns error messages with more explanation which is easy for novice R users to understand them. In base R, one of the most common error encountered is $ operator is invalid for atomic vectors.
This error appears when you try to use an element of an atomic vector using the $ operator. Let’s call atomic vector as character/numeric vector which most R programmers are familiar with. There are 2 more types of atomic vectors – logical and integer.
Let’s understand it via examples. See them below
# Numeric Vector
numVec
# Character Vector
charVec
# Integer Vector
intVec
# Logical Vector
logicalVec
You can check if a vector is an atomic or not by using is.atomic(numVec). It returns TRUE if it is an atomic vector else FALSE.
Let’s name the numeric vector using names() function
names(numVec)
numVec
A B C
3.0 2.5 5.6
When we try to access first value by using name A using dollar $ operator, it returns this error.
numVec$A
Error in numVec$A : $ operator is invalid for atomic vectors
There are three ways we can fix this error.
Solution 1 : Use Double Brackets
We can use double brackets [[ ]] to access element by name from an atomic vector. Make sure to use quotes in the name as it is a string.
numVec[[‘A’]]
[1] 3
Yes we can use single bracket [ ] for this task but the output will be in a different format. It returns named number instead of just the number. Refer the ouput below.
numVec[‘A’]
A
3
We can remove name like this unname(numVec[‘A’]). Hence it’s better to use double brackets as single bracket complicates things unless you want named number.
Solution 2 : Use getElement( )
getElement( ) follows this syntax style – getElement(object, name). It was designed for this kind of problem statement only. getElement(numVec, ‘A’)
[1] 3
Solution 3 : Convert to Dataframe
This is not a recommended solution but the intend is to show you another way to solve this problem using data.frame( ). We need to transpose before wrapping the vector in data.frame( ) as we need data to be stored in a single row with name of vector as column names instead of 3 rows.
myDF myDF$A
[1] 3
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