How to check if a column exists in a matrix or data frame?

Question

Is there a way to check if a column exist in a matrix or data.frame? For example: TableA ``` Name Age Address Contact No. Ben 12 CA 1234567 ``` How can I check if a column "Gender" or "Age" exist before I process a row? Thanks

Accepted Answer

I hope you realise that columns `"Gender"` or `"Age"` either do or don't exist for all rows in the data frame?

An easy way to check is to take the names of the data frame and compare the columns you are inetrested with the names to see if they are included in that set. For example, some data as per your question:

```
df <- data.frame(Name = "Ben", Age = 12, Address = "CA", ContactNo = 1234567)
```

Note the `names` attribute for the data frame `df`:

```
names(df)

> names(df)
[1] "Name"      "Age"       "Address"   "ContactNo"
```

Then you can check to see if the variables of interest are in the set of variables in the data frame:

```
c("Gender", "Age") %in% names(df)

> c("Gender", "Age") %in% names(df)
[1] FALSE  TRUE
```

For a matrix, you need the `colnames` attribute, accessed via the `colnames()` extractor function, instead of the `names` attribute and `names()`.

How to check if a column exists in a matrix or data frame?

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