selecting certain rows from R data frame

Question

I have this huge data frame that has servernames, Date, CPU, memory as the headers. There are multiple servers names. I would like to be able to select certain server name order by the date column and create time serious graphs

this is a small subset of the data frame:

     Hostname                Date     5 60 61 CPUAVG CPUAVG+Sev CPUMaximum MemoryAVG
1 server1 2012-01-29 01:00:00 23.79 NA NA   2.33       0.72       2.33     23.76
2 server1 2012-01-29 02:00:00 23.91 NA NA   2.86       2.38       2.86     23.82
3 server1 2012-01-29 03:00:00 25.65 NA NA   6.25       9.59       6.25     24.85
4 server2 2012-01-29 04:00:00 26.30 NA NA  18.41      31.09      18.41     25.87
5 server3 2012-01-29 05:00:00 24.33 NA NA   1.92       0.42       1.92     24.24
6 server3 2012-01-29 06:00:00 24.40 NA NA   2.65       1.79       2.65     24.31

Jeff Allen · Accepted Answer · 2012-02-02 15:42:06Z

3

Checkout the 'subset' command.

thisServer <- subset (servers, Hostname="server1")

Then to order the rows

thisServerSorted <- thisServer[order(thisServer$Date),]

Then you can plot from there.

answered Feb 2, 2012 at 15:42

Jeff Allen

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6 Comments

Justin Over a year ago

you can also subset directly: servers[servers$Hostname=='server1',]

george willy Over a year ago

thank you so much. How would I do this if there was a large data set and I needed to automatically retreive distinct server names order by date graph them all in one chart.

Matt Dowle Over a year ago

"Large" means different things to different people. It would realy help if you just said how many GB it was, or how many rows and columns, or something like that.

Jeff Allen Over a year ago

Quick answer would be to use the split() command. More robust answer would be to use something like ddply (see stackoverflow.com/questions/1395191/… )

george willy Over a year ago

large meaning there are 100 different servers when I have to real the file and create graphs based on each server name having a different line in the chart. I need to be able to dynamically choose the server name, not knowing ahead of time what it is. The below example assumes that I know the server names.

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Thierry · Accepted Answer · 2012-02-02 16:13:41Z

2

#convert Date to a date field (if needed)
library(lubridate)
servers$Date <- ymd_hms(servers$Date)
#select the servers you need
SelectedServers <- subset(servers, Hostname %in% c("server1", "server3"))
library(ggplot2)
#no need for sorting with ggplot2
ggplot(SelectedServers, aes(x = Date, y = CPUAVG, colour = Hostname)) + geom_line()
ggplot(SelectedServers, aes(x = Date, y = CPUAVG)) + geom_line() + facet_wrap(~Hostname)

answered Feb 2, 2012 at 16:13

Thierry

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