R 3.0.2 - How to create intervals and group another variable in those intervals?

n <- 1000
x <- data.frame(speed = runif(n, 0, 85.53)

# create interval for speed
int <- seq(0, max(x) + 4.5, by = 4.5)
# split the data and find average of spacing
tapply(x$spacing, cut(x$speed, int), mean)

# find the average speed
tapply(x$speed, cut(x$speed, int), mean)

Thanks Jim. You now provided me with the average of spacing but how can I
find the average of speed for every speed interval? I am a newbie in R,
sorry for my stupid questions


Umair Durrani
email: umairdurrani at outlook.com

Date: Wed, 6 Nov 2013 12:22:50 -0500
Subject: Re: [R] R 3.0.2 - How to create intervals and group another
variable in those intervals?
From: jholtman at gmail.com
To: umairdurrani at outlook.com
CC: r-help at r-project.org

should of had in the script:


int <- seq(0, max(x$speed) + 4.5, by = 4.5)



Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.


On Wed, Nov 6, 2013 at 12:19 PM, jim holtman <jholtman at gmail.com> wrote:

Is this what you are after:

n <- 1000
x <- data.frame(speed = runif(n, 0, 85.53)

+ , spacing = rnorm(n)
+ )

# create interval for speed
int <- seq(0, max(x) + 4.5, by = 4.5)
# split the data and find average of spacing
tapply(x$spacing, cut(x$speed, int), mean)

(0,4.5] (4.5,9] (9,13.5] (13.5,18] (18,22.5]
(22.5,27] (27,31.5] (31.5,36]
0.27840783 -0.08349567 -0.10659408 -0.01476840 -0.08773255
-0.06643826 0.21873016 0.17627232
(36,40.5] (40.5,45] (45,49.5] (49.5,54] (54,58.5]
(58.5,63] (63,67.5] (67.5,72]
-0.16568350 -0.15458191 -0.04909331 -0.01179396 0.25022296
-0.27553812 -0.14927483 -0.21000177
(72,76.5] (76.5,81] (81,85.5]
-0.09884137 -0.08459709 0.02864456

plotting is left as an exercise for the reader, but given the averages
above, you can find the midpoints easily.

Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.


On Wed, Nov 6, 2013 at 10:48 AM, umair durrani
<umairdurrani at outlook.com> wrote:

I have two columns for speed ('Smoothed velocity') and Spacing. What I
want to do is to first create the intervals of speed (minimum value=0, max
value= 85.53), group the Spacing values falling in a particular Speed
interval, find the average of the Spacing for an interval and finally plot
the average spacing of each interval against the mid-point of the Speed
interval. I want to have fixed intervals of 4.5 feet per second, i.e. 0-4.5,
4.5-9,......xx-85.53.After hours of search I found a function for creating
intervals called classIntervals() but I can't figure out how to create fixed
intervals of 4.5. Here is what I tried:classIntervals(s21[,'Smoothed
velocity'], style='fixed', fixedBreaks=4.5)But the results were unexpected
and there was a Warning message:In classIntervals(s21[, "Smoothed
velocity"], style = "fixed", fixedBreaks = 4.5) :
variable range greater than fixedBreaksEven after intervals are
created, I need to group spacing and find the avg. for every interval. How
can I do this? I have tried what I could, please help

Umair Durrani

email: umairdurrani at outlook.com

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