Aligning Columns with knitr kable function

You want to feed kable a vector of alignment strings equal to the number of columns. As mentioned in the help file,

the alignment of columns: a character vector consisting of 'l' (left), 'c' (center) and/or 'r' (right); by default, numeric columns are right-aligned, and other columns are left-aligned; if align = NULL, the default alignment is used.

Here is a reproducible example.

Without any alignment values, character columns are left-aligned and numeric columns are right-aligned as you can see below.

library(knitr)kable(head(mtcars[1:5]))

which returns

|                  |  mpg| cyl| disp|  hp| drat||:-----------------|----:|---:|----:|---:|----:||Mazda RX4         | 21.0|   6|  160| 110| 3.90||Mazda RX4 Wag     | 21.0|   6|  160| 110| 3.90||Datsun 710        | 22.8|   4|  108|  93| 3.85||Hornet 4 Drive    | 21.4|   6|  258| 110| 3.08||Hornet Sportabout | 18.7|   8|  360| 175| 3.15||Valiant           | 18.1|   6|  225| 105| 2.76|

To get the numeric columns center-aligned, while keeping the character column right aligned, I used the following.

kable(head(mtcars[1:5]), align=rep('c', 5))|                  | mpg  | cyl | disp | hp  | drat ||:-----------------|:----:|:---:|:----:|:---:|:----:||Mazda RX4         | 21.0 |  6  | 160  | 110 | 3.90 ||Mazda RX4 Wag     | 21.0 |  6  | 160  | 110 | 3.90 ||Datsun 710        | 22.8 |  4  | 108  | 93  | 3.85 ||Hornet 4 Drive    | 21.4 |  6  | 258  | 110 | 3.08 ||Hornet Sportabout | 18.7 |  8  | 360  | 175 | 3.15 ||Valiant           | 18.1 |  6  | 225  | 105 | 2.76 |

The following text, if copied into an .Rmd file, will return the table, formatted as desired as a pdf file.

---title: "Untitled"output: pdf_document---this thing```{r table1, as.is=TRUE}library(knitr)kable(head(mtcars[1:5]))```is not a centered table, while this thing```{r table2, as.is=TRUE}kable(head(mtcars[1:5]), align=rep('c', 5))```is a centered table.

Even easier: kable(mtcars, align = "l") works just fine!

You can also use the length function to create a vector for all rows in a vector/dataframe without having to hard code a length. The example below left-aligns all the columns in the mtcars data frame no matter the length.

 kable(mtcars, align=rep('l', length(mtcars[,1])))