Add "sapply function" guide to R guides (#36010)

* Add "sapply function" guide to R guides

* Add review suggestions on formatting

guide/english/r/functions/sapply-function/index.md

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+---
+title: sapply() Function
+---
+## sapply() Function
+
+The `sapply()` function is part of a family of `apply()` functions that aide in manipulating data. It takes 2 or more parameters and it returns a vector or matrix. The first parameter could be a vector or a data frame. The second parameter is usually a function you want to use along the elemnts of columns of the first parameter. 
+
+You can use sapply to get the max of every column in a data frame as a vector.
+
+```r
+df <- data.frame(a = c(49, 12, 32, 21, 16), b = c(22, 39, 8, 54, 26))
+df
+#      a    b   
+# 1   49   22  
+# 2   13   39   
+# 3   32    8   
+# 4   21   54  
+# 5   16   26  
+df <- sapply(df, max)
+df
+#  a   b
+# 49  54  
+```
+
+In the above example, the data frame itself is transformed by using `sapply()` on it directly.
+
+You can also use `sapply()` within a function.
+
+```r
+df <- data.frame(a = c(49, 12, 32, 21, 16), b = c(22, 39, 8, 54, 26))
+df
+#      a    b   
+# 1   49   22  
+# 2   13   39   
+# 3   32    8   
+# 4   21   54  
+# 5   16   26  
+
+# Function to get the max number of every column for any dataframe
+colMax <- function(data) sapply(data, max)
+
+# maxes is a vector with the max number of every column in data frame df
+maxes <- colMax(df)
+maxes
+#  a   b
+# 49  54
+```
+
+You can use various different built in R functions such as `sqrt`, `min`, or `mean` with `sapply()` function.
+
+## Resources
+
+- [Study Trails](http://www.studytrails.com/r/core/control_structures_r_apply_functions/)
+- [bookdown](https://bookdown.org/rdpeng/rprogdatascience/loop-functions.html)
+- [DataCamp](https://www.datacamp.com/community/tutorials/r-tutorial-apply-family)
+- [Advanced R](http://adv-r.had.co.nz/Functionals.html)
+
+