Apply function in R

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I am new to R and I have heard a lot about the apply function.

Can someone list down the advantages of apply function?

Thanks.
Jul 9, 2018 in Data Analytics by DataKing99
• 8,130 points
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2 answers to this question.

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The apply function allows us to make entry-by-entry changes to data frames and matrices.

The usage in R is as follows:

apply(X, MARGIN, FUN, …)

where:

X is an array or matrix;

MARGIN is a variable that determines whether the function is applied over rows (MARGIN=1), columns (MARGIN=2), or both (MARGIN=c(1,2));

FUN is the function to be applied.

If MARGIN=1, the function accepts each row of X as a vector argument and returns a vector of the results. Similarly, if MARGIN=2 the function acts on the columns of X. Most impressively, when MARGIN=c(1,2) the function is applied to every entry of X.

Advantage:

With the apply function, we can edit every entry of a data frame with a single line command. No auto-filling, no wasted CPU cycles.

answered Jul 9, 2018 by CodingByHeart77
• 3,690 points
0 votes

apply


Description: “Returns a vector or array or list of values obtained by applying a function to margins of an array or matrix.”

We know about vectors/arrays and functions, but what are these “margins”? 

Simple: either the rows (1), the columns (2) or both (1:2). By “both”, we mean “apply the function to each individual value.” An example:

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

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20

21

# create a matrix of 10 rows x 2 columns

m <- matrix(c(1:10, 11:20), nrow = 10, ncol = 2)

# mean of the rows

apply(m, 1, mean)

 [1]  6  7  8  9 10 11 12 13 14 15

# mean of the columns

apply(m, 2, mean)

[1]  5.5 15.5

# divide all values by 2

apply(m, 1:2, function(x) x/2)

      [,1] [,2]

 [1,]  0.5  5.5

 [2,]  1.0  6.0

 [3,]  1.5  6.5

 [4,]  2.0  7.0

 [5,]  2.5  7.5

 [6,]  3.0  8.0

 [7,]  3.5  8.5

 [8,]  4.0  9.0

 [9,]  4.5  9.5

[10,]  5.0 10.0

answered Jul 10, 2018 by zombie
• 3,710 points

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