I am not able to apply if loop to a dataframe in r programming

Question

I have a Blood pressure Dataframe with the below data.

   Name Age M.F Blood.Pressure
1     A  40   M            110
2     B  55   F            112
3     C  51   M            144
4     D  14   M            134
5     E  48   M             90
6     F  78   M             85
7     G  21   F            135
8     H  59   M            150
9     I  32   F             98
.....

I need to check B.P. of each record and based on the values, I have to create a new column with the strings ("Low","Normal","High") corresponding to B.P. I am using the below code to do that.

excel <- read.csv("SampleCSVFile.csv", header=T)
df1 <- data.frame(excel)
df1

for(i in length(df2$Blood.Pressure))
{
  if (df1$Blood.Pressure > 80 & df1$Blood.Pressure < 120)
  {
      df1$is.cond <- c("Low")
  }

  else if(df1$Blood.Pressure > 120 & df1$Blood.Pressure < 140)
  {
      df1$is.cond <- c("Normal")
  }
  else if(df1$Blood.Pressure > 140)
  {
      df1$is.cond <- c("High")
  }
}
df1

But this is the output that I am getting.

   Name Age M.F Blood.Pressure is.cond
1     A  40   M            110     Low
2     B  55   F            112     Low
3     C  51   M            144     Low
4     D  14   M            134     Low
5     E  48   M             90     Low
6     F  78   M             85     Low
7     G  21   F            135     Low
8     H  59   M            150     Low
9     I  32   F             98     Low
10    J  63   M            150     Low

It is not checking each row, it just checks the first Blood pressure value, and based on that it assigns the string to all the rows. can you please help ?

That's because you're not even using looping variable 'i' anywhere. And please read the policy of how to ask good questions here : stackoverflow.com/questions/ask/advice? — Virag Swami
– Virag Swami, Commented Jun 29, 2016 at 5:20
Or Excel? Or CSV? Don't use tags just because they might be suggested. — Gregor Thomas
– Gregor Thomas, Commented Jun 29, 2016 at 5:54

Gregor Thomas · Accepted Answer · 2016-06-29 05:49:11Z

4

You don't need a loop. This is a vectorized way to do things:

# initialize column
df1$is.cond = NA_character_

df1$is.cond[df1$Blood.Pressure > 80 & df1$Blood.Pressure < 120] = "Low"
df1$is.cond[df1$Blood.Pressure > 120 & df1$Blood.Pressure < 140] = "Normal"
df1$is.cond[df1$Blood.Pressure > 140] = "High"

However, for binning data like this the built-in function cut does all the work for us:

df1$is.cond.cut = cut(df1$Blood.Pressure,
                      breaks = c(-Inf, 80, 120, 140, Inf),
                      labels = c("unknown", "Low", "Normal", "High"))

In your method (and in my first example), because you use < rather than <=, no value will be assigned to blood pressures exactly on the threshholds. You might want to change that. cut defaults to intervals that are "closed on the right", meaning that a value of 120 would be considered Low. You can change this behavior by giving it the argument right = F.

answered Jun 29, 2016 at 5:49

Gregor Thomas

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1 Comment

Chethanraj Rao Over a year ago

Thanks a lot for this answer!

Virag Swami · Accepted Answer · 2016-06-29 06:16:48Z

1

How about a cleaner solution :

df1$is.cond <- ifelse(df1$Blood.Pressure > 80 & df1$Blood.Pressure < 120, "Low",
          ifelse(df1$Blood.Pressure > 120 & df1$Blood.Pressure < 140, "Normal", 
             ifelse(df1$Blood.Pressure > 140, "High" , "None")))

edited Jun 29, 2016 at 6:16

answered Jun 29, 2016 at 5:45

Virag Swami

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1 Comment

Chethanraj Rao Over a year ago

I got this idea as soon as I posted this question. Anyway thanks for your suggestion!.

Pankaj Kaundal · Accepted Answer · 2016-06-29 05:46:30Z

1

See if that's what you needed .

df1 <- read.csv("file_to_read.csv",T,"~")


for(i in 1:nrow(df1))
{
  if (df1$Blood.Pressure[i] > 80 & df1$Blood.Pressure[i] < 120)
  {
    df1$is.cond[i] <- c("Low")
  }

  else if(df1$Blood.Pressure[i] > 120 & df1$Blood.Pressure[i] < 140)
  {
    df1$is.cond[i] <- c("Normal")
  }
  else if(df1$Blood.Pressure[i] > 140)
  {
    df1$is.cond[i] <- c("High")
  }
}

> df1
  Name Age M.F Blood.Pressure is.cond
1    A  40   M            110     Low
2    B  55   F            112     Low
3    C  51   M            144    High
4    D  14   M            134  Normal
5    E  48   M             90     Low
6    F  78   M             85     Low
7    G  21   F            135  Normal
8    H  59   M            150    High
9    I  32   F             98     Low

edited Jun 29, 2016 at 5:46

answered Jun 29, 2016 at 5:35

Pankaj Kaundal

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1 Comment

Chethanraj Rao Over a year ago

Thanks a lot for your suggestion. This is what I wanted.

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