CODEWITHSUNDEEP
r
user2833448
user2833448

Reputation: 25

Account for change in variable in while loop

My data.frame Calculations is structured as follows:

head(Calculations)

     Name        x        y  Sample  Time
1  Thomas  26.6627 -12.3782       1  0.01
2  Thomas  26.6564 -12.3711       2  0.02
3  Thomas  26.6497 -12.3635       3  0.03
4 Caitlin  28.6423 -14.3555       1  0.01
5 Caitlin  28.6353 -14.3472       2  0.02
6 Caitlin  28.6269 -14.3385       3  0.03

Whereby SampleRate <- 100 and k <- as.integer(SampleRate) whilst m_velocity<- matrix(NA, length(Calculations$x))

I wish to run the following while loop to calculate velocity over time:

attach(Calculations)
i <- 2
while(i < length(x) - k){
  m_velocity[i] <- sqrt(sum((x[i] - x[i-1]) ^2, (y[i] - y[i-1]) ^2)) / (1/SampleRate)
  i <- i+1
}

However, this does not restart for each Name. For example, the first velocity entry for Caitlin would be NA and not calculated from the X and Y coordinates from Thomas.

UPDATED I used the following code to obtain Velocity:

Calculations %>%
  arrange(Name) %>%
  group_by(Name) %>%
  mutate(Velocity = sqrt( (x - lag(x) )^2 + (y - lag(y) )^2 ) * SampleRate)

but when I checked the first entry of Sample for each Name using ddply(Calculations,.(Name),function(x) head(x,1)) velocity is still being calculated from the previous person's X and Y coordinates. Any suggestions?

SOLVED My issue was stemming from first loading dplyr then plyr which creates issues as stated here.

Upvotes: 1

Views: 144

Answers (1)

bramtayl
bramtayl

Reputation: 4024

You can do this without a while loop.

library(dplyr)

calculations %>%
  group_by(Name) %>%
  mutate(velocity = sqrt( (x - lag(x) )^2 + (y - lag(y) )^2 ) * SampleRate)

Upvotes: 3

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