Levels: This another Nvarchar text This is Nvarchar text Getting data from TXT / CSV files
So changing the original SQL query to cast all the values: df This is rather unexpected, since the SQL Server data types again are not working for R environment. Both are factors, but NULL or NA values can be treated respectively. Same logic applied to text1 and text2 fields. So this means, that handling NA is not only about the “Not Available” but also the type of “Not Available” information and each of these needs special attention, otherwise when doing some calculations or functions, coerce error will be constantly emerging.ĭata imported using SQL Server can be used as normal dataset imported in R in any other way: #making some elementary calculations And only the is logical object, that is the Not Available information. What is presented in SQL Server as NULL value, it is represented in R as NA which is a logical type, but not the real NA.
When put side-by-side the output from SQL Server and output in R, there are some differences: General understanding of all values by simply using following code: #reading documentation on all data types: Infinite also tells you that the value is not missing and a number!Īll four null/missing data types have accompanying logical functions available in base R returning the TRUE / FALSE for each of particular function: is.null(), is.na(), is.nan(), is.infinite(). Inf is a reserved word and is – in most cases – product of computations in R language and therefore very rarely a product of data import. Inf and -Inf stands for infinity (or negative infinity) and is a result of storing either a large number or a product that is a result of division by zero.
NaN stands for Not A Number and is a logical vector of a length 1 and applies to numerical values, as well as real and imaginary parts of complex values, but not to values of integer vector. NA and “NA” (as presented as string) are not interchangeable. NA is a logical constant of length 1 and is an indicator for a missing value.NA (capital letters) is a reserved word and can be coerced to any other data type vector (except raw) and can also be a product when importing data. In R language, NULL (capital letters) is a reserved word and can also be the product of importing data with unknown data type. NULL is an object and is returned when an expression or function results in an undefined value. R language supports several null-able values and it is relatively important to understand how these values behave, when making data pre-processing and data munging.
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