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I'm using R and have loaded data into a data frame using read.csv(). How do I determine the data type of each column in the data frame?

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You can use the following ways to determine the data types of columns in a data frame:

Using str() Function:

str function compactly displays the structure of an arbitrary R object.

For example:

To display the structure of iris dataset

str(iris)

'data.frame': 150 obs. of  5 variables:

 $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...

 $ Sepal.Width : num  3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...

 $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...

 $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...

 $ Species     : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1 1 1 1 1 ...

Using sapply() Function

sapply() is used to apply a function over a list or vector.

For example:

sapply(iris, class)

Sepal.Length  Sepal.Width Petal.Length  Petal.Width      Species 

   "numeric"    "numeric"    "numeric"    "numeric"     "factor" 

sapply(iris, typeof)

Sepal.Length  Sepal.Width Petal.Length  Petal.Width      Species 

    "double"     "double"     "double"     "double"    "integer"

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