## How to find the index of an element in a vector in R?

Updated on 06-Jul-2020 14:15:42
There are three ways to find the index of an element in a vector.Example> x x [1] 8 10 9 6 2 1 4 7 5 3Using which> which(x == 6)[[1]] [1] 4Here we found the index of 6 in vector x.Using match> match(c(4,8),x) [1] 7 1Here we found the index of 4 and 8 in vector x.Using which with %in% > which(x %in% c(2,4)) [1] 5 7Here we found the index of 2 and 4 in vector x.

## How to randomly select a fixed number of rows without replacement from a data frame in R?

Updated on 06-Jul-2020 14:14:37
This can be done simply by using sample function.Example> df = data.frame(matrix(rnorm(20), nrow=5)) > df X1 X2 X3 X4 1 -0.3277833 -0.1810403 0.2844406 -2.9676440 2 0.8262923 0.4334449 0.4031084 -1.9278049 3 -0.1769219 -0.1583660 -0.2829540 -0.1962654 4 1.0357773 0.9326049 0.3250011 -1.8835882 5 -1.0682642 -0.6589731 -0.4783144 -0.2945062Let’s say we want to select 3 rows randomly then it can be done as follows −> df[sample(nrow(df), 3), ] X1 X2 X3 X4 2 0.8262923 0.4334449 0.4031084 -1.9278049 1 -0.3277833 -0.1810403 0.2844406 -2.9676440 5 -1.0682642 -0.6589731 -0.4783144 -0.2945062

## How to rename a single column in an R data frame?

Updated on 06-Jul-2020 14:11:56
We can do this by defining the newname as shown below −> Samp Samp sample.1.100..10. 1 47 2 63 3 57 4 16 5 53 6 7 7 54 8 2 9 13 10 14 > colnames(Samp) Samp Sampled Values 1 47 2 63 3 57 4 16 5 53 6 7 7 54 8 2 9 13 10 14 Since we only have one column in the data frame, so it is sufficient to use the object name.

## How to add zeros before numbers in R?

Updated on 06-Jul-2020 14:09:36
The easiest way to add zeros before numbers is by using paste0 functionExample> ID Gender Lens data data ID Gender Lens 1 25499 1 0.8 2 25500 2 1.2 3 25501 2 1.0 4 25502 1 2.0 5 25503 2 1.8 6 25504 1 1.4Let’s say we want to add 00 before every ID.It can be done by using paste0 function as follows −> IDs newdata newdata IDs Gender Lens 1 0025499 1 0.8 2 0025500 2 1.2 3 0025501 2 1.0 4 0025502 1 2.0 5 0025503 2 1.8 6 0025504 1 1.4

## How to sum a variable by factor levels in R?

Updated on 06-Jul-2020 14:08:10
We can do this by using aggregate function or with the help tapplyExample> x x Category Frequency 1 Graduation 12 2 Graduation 19 3 Post-Graduation 15 4 Graduation 20 5 PhD 25 6 Post-Graduation 13 7 PhD 14Using aggregate> aggregate(x$Frequency, by=list(Group=x$Category), FUN=sum) Group x 1 Graduation 51 2 PhD 39 3 Post-Graduation 28 Using tapply > tapply(x$Frequency, x$Category, FUN=sum) Graduation PhD Post-Graduation 51 39 28

## How to extract columns of a data frame in R using dplyr package?

Updated on 06-Jul-2020 14:06:29
Example> x y z df library(dplyr) > df %>% select(y, z) y z 1 1.486720e-06 7.888609e-31 2 1.338302e-04 7.888609e-29 3 4.431848e-03 3.904861e-27 4 5.399097e-02 1.275588e-25 5 2.419707e-01 3.093301e-24 6 3.989423e-01 5.939138e-23 7 2.419707e-01 9.403635e-22 8 5.399097e-02 1.262774e-20 9 4.431848e-03 1.467975e-19 10 1.338302e-04 1.500596e-18 11 1.486720e-06 1.365543e-17 12 6.075883e-09 1.117262e-16 13 9.134720e-12 8.286361e-16 14 5.052271e-15 5.609229e-15 15 1.027977e-18 3.485735e-14 16 7.694599e-23 1.998488e-13 17 2.118819e-27 1.061697e-12 18 2.146384e-32 5.246031e-12 19 7.998828e-38 2.419003e-11 20 1.096607e-43 1.043991e-10 21 5.530710e-50 4.228163e-10Second> select(df, y, z) y z 1 1.486720e-06 7.888609e-31 2 1.338302e-04 7.888609e-29 3 4.431848e-03 3.904861e-27 4 5.399097e-02 1.275588e-25 5 2.419707e-01 3.093301e-24 6 ... Read More

## How to concatenate strings in R?

Updated on 06-Jul-2020 13:00:44
Concatenation can be done by using paste function in R.Example> paste("I", "Love", "R", sep=" ") [1] "I Love R"If we want to specify characters between words then it can be done by using collapse argument as follows −> x x [1] "I" "Love" "R" > paste(x, collapse="-") [1] "I-Love-R"

## How to find mode(s) of a vector in R?

Updated on 06-Jul-2020 12:58:40
Just like mean and median there is no in-built function in R to find the mode.We can make use of the following user created function for this purpose> Modes

## How to create a frequency table of a vector that contains repeated values in R?

Updated on 06-Jul-2020 12:57:49
We can do this by using table function with as.data.frameExample> X as.data.frame(table(X)) X Freq 1 21 2 2 23 3 3 24 1 4 25 5 5 34 2 6 47 2 7 64 1 8 69 5 9 70 1

## How to change the column names and row names of a data frame in R?

Updated on 06-Jul-2020 12:56:42
We can colnames function to change the column names and rownames function to change the row names.Example> df df ID Salry 1 1 10000 2 2 30000 3 3 22000 4 4 27000 5 5 18000 > colnames(df) df EmployeeID Salary 1 1 10000 2 2 30000 3 3 22000 4 4 27000 5 5 18000 > rownames(df)
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